Keene Weather

Final Pattern Change

2011-01-16T00:51:00.003-05:00

Unfortunately, due to work and college, my time available to maintain the website has become limited. Rather than produce rushed, half-hearted forecasts, I've decided to retire the website. I've had a great time working on the site, and hearing the feedback, whether positive or negative (usually correlated to whether or not we had a snowday). Thanks everyone for your support and enthusiasm!

Special thanks to Nate Selvidio, who started the domain www.KeeneWeather.com for me.

I've started a twitter account, which I should be able to update more readily without the time needed for other maintenance.

http://twitter.com/KeeneWeather

Brief icy conditions possible tomorrow morning

2010-11-21T14:01:00.000-05:00

As high pressure slides to our east tonight, winds will turn to the southeast, adding moisture to the low levels. A storm system currently moving through the Midwest will track into the Great Lakes region tonight, pushing a warm front toward the region from the southwest, providing a focus for lift and light precipitation.

Forecast soundings indicate a dry layer above the lower moist layer which is a classic indication of drizzle. Surface temperatures will start off in the 20's tonight, and rise into the low 30's by mid morning, allowing for freezing drizzle. As mid levels moisten a little more by noon, we may see brief light snow in central and northern NH, before flipping to rain.

No accumulation is expected, and this likely will not pose any issues. Just a heads up.

Looking ahead, adverse weather conditions appear likely for Thursday (Thanksgiving) night into Friday. Wintry precipitation is a distinct possibility, although there're still equal chances that it turns out as all rain. More details (and more confidence in those details) tomorrow.

Wintry conditions likely tomorrow morning

2010-11-07T19:35:00.004-05:00

Precipitation will be backing from east to west across the state this evening, with a rain/snow mix moving into SW NH by midnight. As the storm intensifies to our east, snow will increase in intensity, mixing with sleet and freezing rain Monday morning. Accumulations of 0.5" to 1" are likely for everyone with up to 2" above 1000'. In addition a light glaze of ice is possible. Surface temperatures will be below freezing, so be prepared for slippery conditions for the AM commute.

There is a slight chance of a delay tomorrow, dependent mainly on the freezing rain.

Wintry precip possible AM Monday

2010-11-07T00:07:00.003-04:00

The trough associated with the storm system last week is now trapped along the east coast between ridging over the Midwest and the northwest Atlantic. As the trough sharpens, intense vorticity will slam against the ridge over the Atlantic, tilting the trough negative and cutting off as an upper low. This low will lift northward toward southern New England, with surface cyclogenesis over the western Atlantic. The surface disturbance will strengthen quickly with the upper level support and get pulled west toward the region.

With the upper low cut off from the mean flow, we won't have a source of cold air to the north, however we will benefit significantly from dynamic cooling as the low moves over head. Model guidance has trended west, placing the low near Boston by noon Monday. So this could be a situation where northern New England experiences rain showers while parts of central Massachusetts and southern New Hampshire are seeing moderate snow!

Based on the latest model trends, the potential does exist for some accumulation over the specified areas, including Keene, Monday morning. Certainly something to keep an eye on.

Significant storm likely Thursday

2010-10-30T11:16:00.005-04:00

In the last few days, model guidance has been keying in on a potential nor'easter on Thursday (11/4). This storm potential coincides with a large scale pattern shift early next week.

General overview:

The strong MJO wave that traversed Indonesia in the last two weeks has been responsible for a surge in tropical cyclone activity in the Western Pacific. The most recent of which is Typhoon Chaba which reached category 4 intensity near 25N, and has since recurved just east of Japan. Upper level divergence and latent heat release has pumped up ridging ahead of the cyclone, triggering a wave train across the Pacific into North America.

In addition, the AAM relative maximum is over, with a strong negative tendency appearing in the northern subtropics. This will propagate northward, having the effect of temporarily weakening the westerlies over the north Pacific. As a result, perturbations in the jet can become more amplified.

Induced ridging over the West Pacific will shift into the central Pacific, supported by La Nina's weakened hadley cell. Downstream, this will amplify a trough over the Gulf of Alaska and ridge over western North America into early next week, with the positive EPO becoming more neutral. Between the ridging to our west and departing storm system on Monday, strong cold air advection will keep temperatures around 5 to 10 degrees below normal over the region.

On Tuesday, model guidance shows some energy from the GOA trough ejecting over top of the ridge into the Northwest Territories. This energy subsequently carves out a trough over central Canada which then digs into the Great Lakes region Wednesday Night and triggers surface cyclogenesis south of New England.

Specifics:

Difficulty in the forecast arises with the interaction of a number of individual short waves.

First to the show is a piece of energy that gets trapped underneath the developing ridge early in the week. Model guidance agrees on developing a weak cut off low over Texas, and most agree on the ridge shoving the low south into the Gulf of Mexico, and not being a significant player. However, the GGEM has been persistent in shifting this low east and phasing it with the trough digging into the eastern US, to make one extremely amplified disturbance displaced to the south. Ultimately this would mean a very warm moist southeast flow over the region with low pressure tracking inland over New York. This solution is being discounted ... for now. The latest run of the ECMWF is leaning in this direction, so unfortunately it cannot be completely ignored.

Next we must deal with the energy within the trough. The operational GFS continues to show very strung out vorticity, with surface cyclogenesis delayed until northern stream phasing occurs. As a result, low pressure develops east of the region and moves northward into Nova Scotia, giving New England only showery precipitation. This solution has little support, and may be less likely than the GGEM.

The ECMWF and UKMET on the other hand phases earlier, resulting in a more amplified solution, with surface low pressure developing east of Delmarva and moving over SE New England. The GFS ensemble mean is also closer to this solution versus the operational GFS, though with notable spread. Both the ECMWF and UKMET show a very dynamic situation with cooling temperatures aloft despite strong southerly flow. This would suggest heavy precipitation rates, falling as snow for much of the interior. In addition, this storm may have some tropical connection depending on the interaction of the trough with Tomas. So moisture will be plentiful.

The possibility does exist for notable snowfall over the interior higher elevations, dependent on the track of the nor'easter. One way or another, we will have a significant storm on our hands this week.

A preliminary look at Winter 2010-11

2010-07-17T11:04:00.004-04:00

The past 9 months has featured a plethora of broken records from the Pacific to the Atlantic to the Arctic, stratosphere, and the Sun. Because of this culmination of meteorological phenomena, a set of analog years could not possibly come close to representing the current state of the atmosphere. A more qualitative approach is better this year.

Reviewing what got us where we are now: Warm waters in the western Pacific steadily collected near the dateline by three significant westerly wind bursts through the autumn and winter months. However, these westerly winds never proceded far into the eastern Pacific where easterly trade winds maintained strength. The Peru current fed colder waters into the extreme eastern Pacific, forcing a west-based El Nino through the winter. A strong west-based El Nino is rare because normally the SST anomalies force a circulation with positive feedback pushing warm waters into the eastern Pacific. In the winter of 2009-10, the ONI hit 1.8C for NDJ, and 1.7C for DJF, indicating a strong warm episode, but the highest SSTAs were locked in the Nino4 region (near the dateline). This season featured the highest monthly Nino4 SSTs ever recorded for October through February. The strong El Nino powered an active subtropical jet that contributed to the multiple historic snow storms in the Mid Atlantic and Southeast US.

After the last westerly wind burst in February, the thermocline began to rise in the central Pacific, with a layer of cool subsurface anomalies developing. The persistent tropical forcing near the dateline subsided in late March, and the MJO became active through the beginning of May. Trade winds reintensified and by the start of May the central Pacific had cooled substantially. Subsurface anomalies began to affect the far eastern Pacific in the middle of May and these surface anomalies subsequently expanded west into the Nino 3 region. By this time, tropical forcing had made a complete 180, with persistent positive OLR and 200mb convergence anomalies near the dateline and negative anomalies in the Indian Ocean and Atlantic.

During the last four weeks, the equatorial Pacific has continued to cool east of 150E. Along and to the west of 150E SSTs have warmed with notable postive anomalies developing. After heat content in the equatorial Pacific steadily decreased between March and early June, it leveled off through early July, though there is new cooling near 140W. What is notable is that higher OHC is slowly expanding eastward in the far western Pacific, near Indonesia. Overall, OHC anomalies are significantly different from 1998 (a proposed analog). The strong west based El Nino last winter compared to the huge east based El Nino of 1997-8 makes the subsequent states of the Pacific two entirely different beasts. In '98 the EPac maintained above normal heat content through October and there was no push of warmer waters in the WPac and consequently that La Nina hung around for a couple more winters.

This year, there is a very clear west push of +OHC near 5N to 10N which is already being reflected in the far WPac at the equator. We should see warming continue in the western Pacific and extend into the central Pacific by late autumn. La Nina will stick around this winter, but it will be EAST based (Nino3 anomaly < Nino4 anomaly) and the DJF ONI will be around -0.8C to -1C. This is also supported by various forecast model ensembles and roll forward methods. Warmest waters in the world right now are near Indonesia. The only change through autumn is perhaps expand east somewhat. This will enhance low level convergence near 150E sustaining MJO waves likely into phase 6 before collapsing. The few times this winter that the MJO survives into the western and central Pacific will be when blocking is most favorable. This is most likely in late December (also supported by La Nina climatology) and February as the La Nina begins to wane.

In the stratosphere, the QBO has set lowest monthly records for the last few months. Westerlies are now descending pretty quickly and will probably reach 30mb by late December. Ozone took a huge hit from high levels of water vapor associated with the strong El Nino, plus supporting the record breaking negative AO. This can be seen this summer manifested through a persistent strongly positive AAO due to the lack of ozone being transported in the BDC. Again the rapid developing La Nina may come to the rescue as water vapor diminishes significantly near the equator and ozone levels recover, which lends support to a possible stratospheric warming. The positive AAO this summer also correlates with above normal arctic heights / -AO next winter. The -QBO easterlies may hang on just long enough to support a SSW in mid to late November, that will significantly disturb the polar vortex. In the last few months, a -PDO SST signature has become better defined in the north Pacific with warm waters stretching across the basin near 40N. The La Nina pattern will certainly help maintain this general feature. The warm waters in the northwest Pacific will not be an easy road for the PV to take, which will more likely end up in the western hemisphere. I like the chances of colder air making it into the CONUS by early December; with moderation toward the middle of December.

In association with the decaying El Nino, global AAM took a plunge in early March. In early June, the AAM bottomed out again, with the 4th strongest GWO in phases 0.5 - 2.5 for the April-August period on record. This boils down to strengthening trade winds in the Pacific lending support to La Nina through positive feedback. Expect the GWO to continue to be displaced toward the La Nina attractor through the autumn and early winter. With this in mind and the prospect of ridging across the north Pacific, there will be multiple strong frictional torque events this winter. Three to five days prior to the event, there will be a significant storm threat from the midwest into the Ohio Valley and northeast as east based -NAO / Atlantic ridge retrogrades west, and SE ridge breaks down. Could see this happen around December 25th, with -NAO pattern and arctic air settling into the Great Lakes and New England region in the end of December / beginning of January, with continued storm threats through the first half of the month. The pattern will lean back toward a La Nina state by the beginning of February, with overrunning snow/ice threats through the first few weeks. Another torque event by the end of the month will bring winter back into the region into March, though with more La Nina influence.

The issue with looking for arctic outbreaks is the enormous heat release from the El Nino last winter. It's been an issue with strong El Ninos in the past, and especially last winter because the anomaly was further west with SST totals the highest of any El Nino. At least the quick transition to La Nina this summer will likely help shift the pattern to a colder arctic through the autumn, with on average stronger mid latitude ridging (as we've already seen this summer) and +AO/+NAO developing for a few months. This will allow colder air and hopefully a recovery in arctic sea ice and snow cover in preparation for mid latitude winter.

In the Atlantic, record high SSTs have been in place since January. The anomaly distribution matched very well with the record breaking -NAO last winter. The vast majority of the tropical and subtropical Atlantic has been well above normal. Every month so far this year has set a new record TNA, and in fact the May TNA set the all time record. The April and May AMO were the highest since 1878 (keep in mind the trend is removed). The June AMO dropped slightly with 1998 taking the lead (oh no! that year again). Also in the same camp is 2005 and 1995. And like those two years, it is no secret that a very active hurricane season is expected this year.

A weak -NAO has continued into the start of the summer, and the signature SSTA tripole in the Atlantic is expected to continue into the Autumn months. The cold midlatitude anomaly is fairly limited in area and amplitude, and is displaced east of the standard location. Warm anomalies in the Gulf Stream are much more robust than other tripole years. One thought to this point is enhanced baroclinicity helping intensify and guide coastal storms in the late autumn and winter. The tripole will help assist blocking patterns to some extent, though the main theme of the 2010-11 winter will likely be an Atlantic ridge pattern. This will be broken up leading into frictional torque events, which will help set up periods of -NAO blocking.

Most of all, I expect this winter to be remembered for abnormal storminess. I expect huge precipitation anomalies from the Ohio Valley into the northern Mid Atlantic and New England. Whether cold air is present will dictate snow, and it shouldn't be too difficult to tap into some semi-arctic air for these systems. General southeast ridge pattern will dominate otherwise, extending into the northeast in early February. Other warm areas will be southern and central plains into the Rockies, with below normal temperatures in the Pacific northwest.

Invest 95L near Florida panhandle

2010-07-02T21:55:00.004-04:00

As we enter the month of July, a big question on the mind of meteorologists is, how active will the tropics be?

Atlantic ocean sea surface temperatures continue to be well above normal, even above 2005 levels. And as a la nina takes over in the equatorial Pacific, westerly shear is overall below normal across the Atlantic. In addition, intrusions of dry air from the Sahara have been limited. These three main factors are all positive for a very active, possibly historic hurricane season. This is nothing new; there's been a strong consensus since the spring for such a possibility.

June is officially the first month of the Atlantic hurricane season and on average only produces a tropical cyclone every few years. Historically it has practically zero correlation to the total season activity. June 2010 was relatively active however, producing Hurricane Alex, the strongest June hurricane in the Atlantic since 1944.

Now onto July, the correlation between monthly activity and total season activity becomes a little stronger. Just think back to 2005, when a record breaking five tropical storms formed, three of which were hurricanes, with two major hurricanes. These numbers obviously gave some foreshadowing to the rest of the record breaking season.

Currently in the Atlantic, there are no monster tropical systems in the making, just a few disturbances to discuss. First and foremost, we have a new invest, 95L just south of the Florida panhandle near 29N/85W. The low is left behind from the trough currently moving offshore (see "heat wave" post), and is nontropical at this time. The is moderate shear and dry air affecting the system, with any thunderstorm activity confined to the south of the circulation. Model guidance brings 95L west and then turns it northwest into Louisiana as a shortwave dives into Texas. At this time, no significant tropical development is expected, but periods of rain and some gusty winds may impact the central Gulf coast within the next four days.

One other noteworthy disturbance is located in the south central Caribbean near 12N/75W. Scattered moderate showers and thunderstorms have been associated with a weak circulation, moving slowly westward. The NAM organizes this tropical wave in the western Caribbean over the next three days. Given a moist, low shear environment, the potential does exist for some slow development. If still in tact, the wave could move into the Bay of Campeche by next weekend. The BoC is often a breeding ground for quick developing tropical storms, so this wave may need to be watched.

Lastly, there is moderate convection associated with a tropical wave near 10N/50W. Most of the convection is within the ITCZ, and no short term development is expected.

Elsewhere across the Atlantic, a strong upper level trough can be seen on water vapor imagery along 60W. This trough is generating strong vertical shear from the NE Caribbean into the central Atlantic.

Heat wave next week

2010-07-02T11:16:00.005-04:00

A prolonged heat wave is likely for much of the Northeast next week.

The upper level trough that brought the refreshing cool/dry weather to the region for the last few days will shift east into the northwest Atlantic by tomorrow. In its place, a broad subtropical ridge will build into the Ohio Valley and eventually the northeast by Sunday. Strong high pressure currently over the Great Lakes will slowly slip southeast, backing winds across the northeastern US. This will unleash a very hot airmass from the southwest.

There are some timing differences between model forecasts as to when the ridge pushes into New England. The GFS in particular is a outlier, developing and retrograding an upper low from the offshore trough, preventing the ridging from building in on Sunday. The GFS still eventually lifts the low north and heights rise by Tuesday.

All other model forecasts keep the low further east and north. 500mb heights rise above 588dm by Monday evening on all guidance, and in some cases reach up to 594dm on Tuesday. This is also supported by the teleconnections as the NAO and AO become more neutral to slightly positive.

The ECMWF brings 850mb temperatures up to 20C into New England as early as Sunday afternoon and becomes very robust with the heat as high pressure shifts further east early next week. Eventually the ridge over the eastern US bridges with ridging over the Atlantic by late Tuesday into Wednesday. During this period, the ECMWF launches 850mb temperatures to between 22C and 25C!!! Most other model guidance is not quite this hot, but there is a consensus for between 17C and 20C every day next week.

Just as a reminder, a heat wave is defined as at least three days with high temperatures of at least 90 degrees. In the last 20 years, Keene has experienced seven heat waves. The longest was July 6-10, 1993. There is overwhelming support for a heat wave next week, possibly lasting five to as long as six days: Sunday through Friday!!! In addition, the peak of the heat wave will likely be Tuesday and Wednesday when high temperatures could possibly reach the upper 90's, to even near 100 in portions of southern New England!! As the Atlantic ridge builds westward, humidity will increase as well. There is a high probability that excessive heat warnings will be issued for a few days next week.

A short wave trough will move through the Great Lakes regions sometime late next week into the following weekend. Model guidance has a wide spread in terms of timing and amplitude, but regardless we should see relief from the heat by the following weekend.

Atlantic Tropical Season Begins

2010-06-04T00:07:00.002-04:00

The 2010 Atlantic hurricane season officially began on Tuesday (June 1). This year promises to be very active.

Sea surface temperatures (SSTs) have been well above normal in the main development region (MDR) of the Atlantic for the 2010 spring. In fact the Tropical Northern Atlantic index (TNA) set an all-time record high in March ... and then again in April! The Atlantic Multidecadal Oscillation (AMO) also set a record for the month of April. These two indices are a strong indication of the hot waters across the tropical Atlantic and the presence of a distinct tripole (warm tropics, cool mid latitudes, and warm high latitudes).

This tripole and consequent above normal MDR SSTs is a result of the persistent strong negative North Atlantic Oscillation (NAO) this past winter. The NAO is the same force that supressed storms south of New England, while making for the snowiest winter on record for much of the Mid Atlantic region. In addition, this winter featured a strong El Nino in the central Pacific. In fact, this was the strongest west based El Nino on record. El Nino drives a zonal overturning cell, effectively an anomaly of the Walker Circulation, which creates subsidence over the MDR, allowing SSTs to warm more than normal.

In the last few months however, the strong El Nino has broken down significantly, and especially in the last four weeks, has made a complete reversal to slightly negative SST anomalies. Easterly wind anomalies have overtaken the equatorial Pacific, although westerlies remain strong in the subtropics and mid latitudes; a sign of El Nino remaining in the atmosphere. Long range forecast models are in agreement that El Nino will continue to die, with a strengthening La Nina into hurricane season. El Nino is associated with increased westerly shear across the Atlantic which is detrimental to tropical development, as it causes the low and mid level circulations to be decoupled. Neutral to weak La Nina conditions have proven to be the best for minimizing shear, which is precisely what is in store.

Also helping to reduce westerly shear will be anomalous easterlies in the stratosphere descending toward the tropopause. This is the product of the Quasi-Biennial Oscillation (QBO) which is a measure of the wind anomaly at 30mb that oscillates with a period of about 28 months. The QBO is currently in the easterly phase with easterly shear in the lower statosphere. By the thermal wind relationship, the easterly shear favors a colder stratosphere and high tropopause height over the equator and the opposite off the equator. The lower tropopause heights has the effect of reduced tropical activity, and this will have some effect through July. However, as the easterlies descend toward the tropospause, westerly shear develops in the stratosphere, raising tropopause heights over the MDR, encouraging tropical formation.

Reducing to intraseasonal time scale, the MJO has reflected a La Nina state for the last month, with a distinct low level divergence pattern over the central Pacific. In addition, the overturning cell favors convection over the Atlantic. This general bias will continue through hurricane season. Following the cycle of the MJO, expect enhanced tropical activity during mid to late July, and again in late August through September (also the climatological peak).

As for predominant track and landfall risk, all signs point toward an above normal Cape Verde season; that is, tropical storms originating in the eastern Atlantic. The seasonal oscillation of the NAO will switch phase coinciding with the peak in activity in late August and September, which is often a period of enhanced risk for an east coast landfall. The east coast has been relatively spared for the last few seasons, but 2010 will be different. The Carolinas, Virginia, as well as New England may be under the gun more than once. In addition, the Gulf of Mexico has warmed dramatically in the last few months and will fuel a number of intense hurricanes, as has been the theme of the last decade.

As for totals, my summer forecast, posted on March 16, specified 19 named storms, 10 hurricanes, and 5 major hurricanes. I continue to have the utmost confidence in these numbers. In addition, as support, the NHC outlook called for 14 to 23 named storms, 8 to 14 hurricanes, and 3 to 7 major hurricanes; and the CSU outlook in June called for 18,10,5. In summary, this season has the highest confidence ever reached for above normal to near record numbers.

Winter making a return?

2010-04-14T00:23:00.001-04:00

April openned with sunny skies and record setting highs in the 80's across New England. This supposedly marked the end of a disappointing winter for the region. However, old man winter is making a last appearance at the end of the week.

A shortwave will swing down from Ontario Thursday Night. A secondary surface low will develop south of New England with a strong cold front extending NW to SE across NY and NJ. The frontal boundary will be a focus for moderate precipitation for much of New England during the day Friday. Model QPF totals are projected around .75"

Precipitation type becomes a concern as high pressure to the north allows a cold northerly ageostrophic flow. At least some mixing with snow appears likely for interior high terrain of New England. In fact, there is growing agreement for decent accumulation. Given the time of the year, it's definitely wise to stay cautious with these situations. We'll have to watch it closely however, because a surprise late season moderate snowfall is entirely possible.

Major flooding ahead for the northeast

2010-03-28T20:26:00.000-04:00

Two rounds of heavy rainfall will affect the northeast tonight through Wednesday.

A strong subtropical jet is shifting east into the Gulf of Mexico, deepening an upper level trough. Surface low pressure is ejecting out of the central Plains into the Ohio Valley, while secondary low pressure has begun to develop in the southeast. A frontal boundary extending north from the low will be the focus for heavy rain tomorrow as a high-PWAT airmass advects north on the low level jet. Totals of 1.5 to 2.5 inches region-wide can be expected through Monday night.

The second round comes as the secondary low turns up the east coast. The upper level trough will close off and capture the surface low, stalling it south of Long Island on Tuesday. In accordance, the low level jet will continue to transport moisture from the Atlantic, and provide a focus for lift over New England. By Wednesday morning, a dry slot working up from the south will shut off the rain across most of the region save a few left over showers. Totals for the entire event will range between 4 and 7 inches, with the axis of heaviest rainfall from New York City through Worcester where upwards of 8 inches is not out of the question. Most of the region is still recovering from major flooding just a week ago. Water levels are still high for most streams, and the soil is saturated. This has the makings of a major flood event for the region.

Potential for accumulating snow AM Friday

2010-03-24T19:43:00.002-04:00

A strong cold front will advance on the region tomorrow afternoon and night; dividing 50's from 20's. A wave of low pressure will move along the front through the central plains into the Mid Atlantic region Thursday night. As colder air plunges south, moisture will be transported north. This will set the stage for rain changing to snow late Thursday night into early Friday morning before drier air moves in. QPF amounts will generally be around .5", but a decent portion will fall as rain. This still leaves us with the potential for one to two inches of wet sloppy snow by Friday morning, primarily in the higher elevations. If colder air works south quicker, it may be more, and so there is a slight chance of a delay on Friday.

Winter's last stand

2010-03-23T19:20:00.001-04:00

Moderate to heavy rain will continue to affect the area tonight as low pressure shifts into the Gulf of Maine. Colder air will filter in behind the storm, possibly changing rain to snow into Wednesday morning across higher elevations. No accumulation is expected.

Skies will clear in the late afternoon Wednesday as the upper low pulls away. Gusty northwest winds can be expected as high pressure builds into the Mid Atlantic region, tightening the pressure gradient. This high will shift offshore south of the region on Thursday, maintaining sunny skies and allowing winds to back to the west. Temperatures should rebound into the upper 50's to near 60, which is about 10 degrees above the normal.

A huge change will come Thursday night into Friday however. A polar vortex will be plunging south into Quebec on Thursday, with a strong cold front slicing through New England Thursday Night. This front will mark a very tight temperature gradient, with the 850mb 0C isotherm draped across Cape Cod, while the -20C isotherm advances into northern Maine! This type of airmass is one we have not seen for a while. In fact, many places in the region have 40 to 50 day streaks of above normal temperatures! High temperatures on Friday will be stuck in the low to mid 30's, while lows Friday night tumble into the teens.

The cold air is not the end of the story. A shortwave will be moving through the central plains and swing into the Mid Atlantic region by Friday morning. This system will never intensify much, as it's flattened by the vortex to the north. However, it will be enough to transport precipitation into Southern New England Friday morning, while temperatures are cold enough to support snow. A few inches of slushy accumulation is entirely possible for areas north of the Mass Pike.

The next storm on the radar will come early next week. Shortwave energy swinging through the central plains next weekend will support intensifying low pressure in the Mid Atlantic by Monday night. This storm will likely be a rain-producer however as cold air retreats northward.

Moving forward toward Easter Weekend, a strong Pacific Jet will nose onshore in the west, amplifying a trough west of the Rockies, and downstream ridging over the Plains by the middle of the next week. This ridging will shift into the east by Easter Weekend, marking a return to above normal temperatures.

SUMMER OUTLOOK 2010

2010-03-16T13:41:00.000-04:00

The autumn to winter of 2009 to 2010 broke multiple records from the tropics to midlatitudes to the arctic.

Starting with the tropics:

Warm waters in the western Pacific steadily collected near the dateline by three significant westerly wind bursts through the autumn and winter months. However, these westerly winds never proceded far into the eastern Pacific where easterly trade winds maintained strength. The Peru current fed colder waters into the extreme eastern Pacific, forcing a west-based El Nino through the winter.

A strong west-based El Nino is rare because normally the SST anomalies force a circulation with positive feedback into the eastern Pacific. 2009-10 was different. The ONI hit 1.8C for NDJ, and 1.7C for DJF, indicating a strong warm episode, but the highest SSTAs were locked in the Nino4 region (near the dateline). This season featured the highest monthly Nino4 SSTs ever recorded for October through February. The strong El Nino powered an active subtropical jet that contributed to the multiple historic snow storms in the Mid Atlantic and Southeast US.

How El Nino is currently progressing:

The anomalies in the central Pacific have begun to diminish in magnitude, as is usual entering boreal spring. Meanwhile the Peru current continues to transport cold waters north, and a negative anomaly has recently developed into the eastern Pacific. Based on recent trends in SSTs, zonal atmospheric momentum and current ENSO models, ENSO should fall back to near neutral this summer, while maintaining an east to west gradient.

Effects on tropical forcing:

This winter has featured persistent tropical forcing near the dateline, with a strong negative OLR signal on the DJF composite, and a nice vertical velocity couplet indicating the meridional overturning cell. This maximum in forcing also coincides nicely with the low level convergence where the WWBs died in their eastward progression. The MJO has consistently lingered in the 7-8-1 territory of phase space. Since no significant reversal in the structure of SST/wind anomalies are expected, there is no reason for this forcing pattern not to continue (a version of Newton's First Law), except for a weaker magnitude through the summer.

Atlantic:

SST anomaly distribution matches very well with the persistent -NAO this winter. The vast majority of the tropical and subtropical Atlantic is above normal right now. In fact, the magnitude of the anomalies competes with even 2005. Negative SST anomalies in the Gulf of Mexico right now, stretching across the middle latitude Atlantic. This is also inline with normal results of a west based El Nino. Should see the Atlantic maintain these warm anomalies, and a general recovery of the Gulf SSTs into the summer.

Atmospheric Angular Momentum:

The last month has featured a significant spike in AAM, with the GWO oscillating around the El Nino attractor. This is a big reversal from the last four years: even the moderate El Nino in 2006-7 saw just a neutral AAM; The last significant +AAM was in 2005. This winter's spike in AAM came largely from strong positive North America mountain torque during the month of January, which was responsible for the pattern change into the February. Currently, the atmosphere is in the process of coming back to equilibrium, with friction torque due to equatorial westerlies, and developing negative mountain torque. With an expected decrease in westerly anomalies in the Pacific, AAM this summer should stabilize near normals, coinciding also with the current long term period of -AAM bias.

Stratosphere:

The QBO dipped below zero in June 2009, and easterly winds continue to steadily lower through the stratosphere. These easterly anomalies assisted with the incredible low index annular mode this winter. January QBO came in at -16.02 and February QBO at -16.98. There has been a deep layer of <-20m/s anomalies above 30mb, that will likely dip down through the summer, and continue affecting the troposphere.

High latitude blocking:

This of course was another major record breaker of the winter. The winter of 2009-10 began with a rapidly falling arctic oscillation, reaching -5.668SD by December 21. Through the rest of the meteorological winter, the AO rose above zero for only two days, and spent an incredible total of 35 days below -4SD! The DJF AO was -3.422, demolishing the previous record low of -2.617 set in 1976-77. The intense ridging over the arctic contributed to the suppression of practically every storm system this winter, with warm temperature anomalies across the subpolar regions and cold anomalies through the middle latitudes.

The height anomaly composite for DJF matches the AO correlation very well with one interesting exception. The below normal heights remain consolidated over the Atlantic Ocean, rather than splitting into two lows over Europe and the eastern US. Trying to match this unique feature to analogs was difficult as the analog composites would always be slanted to either the US or Europe.

The AO has already recovered so far this spring, and will likely avoid the extremeties seen this winter, but with upper level easterly anomalies continuing through the summer, a low index annular mode should redevelop into the summer. Because the summer features shorter atmospheric waves, the way the annular mode affects surface conditions can be variable, and hard to pin down, but factoring tropical forcing into the equation can help.

Soil moisture:

Soil moisture has been shown to have a significant effect on boundary layer temperatures in the summer, with wetter areas having a bias toward cooler temperatures. The Mid Atlantic in particular is entering the spring with wet departures from normal. Eastern Texas up through Missouri and into the Dakotas also have high soil moisture anomalies. The immediate Great Lakes region and portions of the west have drier than normal conditions going into the spring.

Putting it all together:

Using composites of analogs based on the various parameters discussed above, as well as some simple extrapolation of winter trends, here's the outlook for this summer:

June -- Mountain torque forces a +PNA pattern. Below normal heights extending into southeast Canada during this period will keep New England on the cooler side. Ridging will dominate western Canada into the Pacific northwest, with below normal heights influencing California, also consistent with a dying El Nino. The warmest temperatures will be centered in the Ohio Valley, extending into the southeast. There is good potential for severe weather episodes from the Ohio Valley into Pennsylvania, New York and Southern New England as disturbances swing underneath the upper low.

July -- A deep trough in the North Pacific will edge east toward Alaska pushing another trough ashore over California, influencing much of the southwest with below normal temperatures. Ridging will amplify over the south, into the Ohio Valley. Severe weather activity will focus over much of the central plains into the Ohio Valley, with weaker remnant activity affecting the northeast.

August -- North Pacific low slides east, with indications that much of Canada will be affected by below normal heights. The California trough shifts into the central Plains, with strong ridging in the east, although suppressed by hints of a -NAO. Above normal temperatures will dominate much of the east, into the Ohio Valley. The upper Plains will see cooler temperatures, extending down toward Texas. Very good signal for severe weather existing from the Ohio Valley into New England. This could be a very active month for the northeast.

Hurricane Season -- A hyperactive season is likely. Many things are coming together to produce one of the more active hurricane seasons on record. It would obviously be very difficult to beat 2005, but something analogous to 1969, 1995, and 2004 is looking good. The QBO is solidly in negative territory and ready to fall some more with easterly wind anomalies dropping into the upper troposphere, reducing vertical wind shear. A dying El Nino in the spring is frequently a precursor to an active hurrican season in the summer and autumn. First, there is a correlation to above normal Atlantic SSTs, which we are already seeing; and second, if the Eastern Pacific continues to cool, then shear is further reduced.

Preliminary numbers: 19 named storms, 10 of which become hurricanes, 5 of which are major hurricanes.

As for highest risk for landfalls, the season will begin with the Gulf coast and Florida peninsula at highest risk, with the East Coast openning up for business into September.

Model guidance shifts west

2010-02-23T13:06:00.001-05:00

A major winter storm is developing for much of the northeast. Model guidance has shifted the inverted trough axis southwest, which in turn is threatening with warmer temperatures, and slightly less QPF. Keene is still looking at QPF around 1.5" through Wednesday night, but around .5" to .75" may fall as rain Wednesday afternoon, and snow will have low ratios. Still, a messy situation will unfold tonight through tomorrow. Further west, in eastern NY, accumulations of 15" to 25" are possible.

Snowfall forecast through Wednesday night: 7" - 11"
For above 1000ft: 10" - 16"

Round 1

2010-02-22T14:22:00.001-05:00

Model guidance continues to advertise robust QPF for Tuesday afternoon through Thursday morning. The exact evolution of the offshore low is still uncertain. The NAM and GFS appear to be suffering from some convective feedback, holding the low further east. Meanwhile, the UKMET, Euro, and CMC all pull the surface low toward New England. This would in fact help reinforce colder air over SNE, as a stronger northern ageostrophic flow develops. Precipitation type issues will definitely still exist Tuesday afternoon and during the day Wednesday up to Rt 2 in Massachusetts. Lower elevations of Keene may mix with rain for a time Wednesday afternoon, but above 1000ft, precip should be all snow.

Any snow accumulation Tuesday afternoon and evening will be on the light side, around 1-3 inches through 10pm. However, snowfall rates will increase after midnight, with heavy snow likely between 4am and 4pm on Wednesday. SREF probabilities are even indicating potential for 2"/hr rates. By 6pm, precipitation should begin to lighten up quickly as dry air moves in at the mid levels. Some light snow or drizzle may continue as the low levels remain saturated.

For Keene,
Total accumulations through 12z Thursday morning: 8-14"
For elevations above 1000ft: 11-17"

Two major snow storms this week?

2010-02-21T21:04:00.002-05:00

Confidence is growing for a major snowfall Tuesday afternoon through Thursday morning for interior New England and eastern NY. Secondary low pressure forming in the southeast tomorrow afternoon will move into the western Atlantic on Tuesday. A strong inverted trough will remain, linking it to the weakening primary low in southern Ontario. This trough will be the focus for continuous moderate to heavy precipitation. Model guidance differs slightly on the axis of maximum QPF but at this time it looks like eastern NY into southwest New England will be in the QPF jackpot. However, precipitation type will be an issue even up into much of Massachusetts. Low level warmth will be hard to overcome with no prominent high to the north. N MA into SW NH will likely remain all snow, but it will be a wet snow with relatively low ratios.

QP totals through Thursday morning from the first storm will be on the order of 1" to 1.75". Translated, we are looking at snowfall totals possibly reaching double digits.

Preliminary forecast for Keene,NH: 8" to 14"

But that's not all, if you call in the next 5 minutes, we will give you a second snow storm absolutely free. That's right, confidence is also increasing for a second low pressure system to develop in the southeast, and essentially be sucked into the deepening upper level vortex near New England. The low will rapidly deepen as upper level energy phases together, and could produce another round of heavy snow for the region. In addition, strong winds are likely for this second event, suggesting the possibility of blizzard conditions. This is all around day 5 right now in the forecast, so confidence is not as high yet. But the potential does exist for snow totals for this week from now through next weekend of 20" to 40".

I will put together some maps either tonight or tomorrow outlining snow totals across the northeast.

Stormy week ahead

2010-02-20T12:38:00.001-05:00

Two storm systems will affect New England Tuesday through Friday with periods of moderate to heavy precipitation. The potential exists for significant accumulations of snow through next weekend. More details to be posted later. An introduction to the synoptic situation is posted on the main page.

Stay tuned.

A very stormy week possible

2010-02-20T12:20:00.001-05:00

This winter has featured a very anomalous pattern, with strong high latitude blocking controlling the storm track. This week, that same pattern continues. However, the upper low east of New England will break down in the beginning of this week, giving it less influence than the last few storms. A strong polar vortex will be diving south through central Canada, controlling the evolution of shortwaves moving through the polar and southern jets.

There are two distinct events that will affect New England.

1) A weak shortwave ejecting out of the southwest will cross over the southern plains tomorrow. Surface low pressure is currently developing in the southern Rockies and will be shifting east-NE toward Missouri by Sunday night. The low will continue to deepen on Monday, while lifting toward the Great Lakes region. Secondary low pressure will form southeast of Delmarva, and lift north, spreading precipitation into the region on Tuesday. Its track is still uncertain, but models have been keying in on a strong inverted trough focusing an area of moderate to heavy precipitation across New England and New York. With the primary low to our northwest, we still have precipitation type concerns, but mainly inside I95. It should be mostly snow for the interior. A strong blocking ridge to the north will keep this whole thing in place through Wednesday night.

2) By Thursday, a second phase will occur with a lobe off the polar vortex, forming a massive closed upper low southwest of New England. Another shortwave ejecting out of the southwest triggers surface cyclogenesis in the southeast US. This next low gets sucked into the vortex over/south of New England, producing another prolonged period of heavy snow and winds through Friday.

A lot can go wrong still. Model guidance has been advertising some very anomalous solutions for a while. And the HPC discussions grow more robust everyday. The current discussion alludes to New England vaulting into Mid-Atlantic-snowfall territory in one leap. This is not a simple nor'easter with simple track adjustments. Very realistically, snowfall totals for next week could be anything between 4" and 40"

Detailed forecasts will begin later tomorrow in the winter weather outlook.

Heavier bands approach

2010-02-16T13:24:00.001-05:00

Well maybe 2" is enough to close every school in NH. I suppose it's that knee-jerk reaction to seeing "snow" in the forecast after a long dry stretch.

Anyway, we still are looking at heavy snow approaching this afternoon. As the upper low shifts south of the region, bands of snow will shift into SNH. Expect this to begin within the next hour and continue through the early evening, accumulating an additional 3 to 5".

00z models and nowcast

2010-02-15T20:56:00.001-05:00

Radar echoes are moving northeast across western CT. Light snow has been reported in NYC and LI, but nothing more than flurries yet in CT. This light snow will work its way north into the area by early tomorrow morning.

00z NAM is coming in notably further south with the track of the mid level low. Consequently dry slot issues are avoided for a lot of the region, but the best lift will be to the south of the Keene area for the morning round of snow. This lends more confidence to the idea of generally only light accumulations through the early afternoon. However, the NAM is very robust with the afternoon-evening round from the CCB. Could see some heavy snow rates through 7pm. Totals of 4" to 7" still on track.

---Snowday Outlook---
Still not much cause for raising numbers. The main round of snow will be later in the afternoon. Put up some early release numbers for fun. In general, light snowfall rates, with relatively warm temperatures will keep roads from getting too bad through the early afternoon. The evening commute could be a different story.

No changes

2010-02-15T18:49:00.000-05:00

An initial burst of snow from warm air advection will accumulate around 2" to 3" through noon. The dry slot should not get as far north as Keene, however precipitation will become light and showery by noon. By mid afternoon, the mid and upper lows will shift east, backing winds to easterly, transporting moisture back into the region. Expect the heaviest snow during this time through 6pm. Snow will lighten up through midnight. Total accumulations in Keene, 4" to 7". So basically looking at a high end advisory event. The NWS continue winter storm watches for SNH. Hillsborough county will likely be upgraded to a warning, but probably not Cheshire county.

---Snowday Outlook---
Again, no changes here. Accumulations by the morning commute will be under an inch; probably no more than half an inch. Snow will generally be light through the school hours, accumulating up to 4" by the end of the schoolday, leaving plenty of time for roads to be tended to. Temperatures will reach the low 30's in the afternoon, which will help roads stay clean as well.

Eastern New England special

2010-02-15T10:15:00.000-05:00

The GFS has made a large shift east in the last 12 hours, stepping more in line with the Euro. In general, looking at the 700mb low passing over LI, powering a conveyor belt of moisture into much of NH and ME, while creating dry slot issues south of the Mass Pike. Model guidance is converging on a significant snow storm for these areas, with moderate snows across northern CT, RI, western MA, VT and eastern NY. There is still a lot of inconsistencies between the american models and international models that will have to be ironed out through today.

Keene will likely be on the southwest edge of the best dynamics and moisture. If the low track shifts a little more east, snow accumulations will not be very impressive. However, at this time, moderate accumulations look good for the area.

Timeline of the event: Light snow should start falling by 5am, continuing through the early afternoon with accumulations around 2" to 3". The heaviest snow will impact the area in the afternoon, tapering back to light snow showers after 6pm. Total accumulations of 4" to 7".

---Snowday Outlook---
Snow accumulations will be spread out through the day, with the heaviest occurring later in the day. Not much will be on the ground in the morning either. So for now, staying with low percentages.

Significant snowfall Tuesday

2010-02-14T16:06:00.000-05:00

An intense mid level wave is currently diving through the central plains, and will be passing through the Ohio Valley during the day tomorrow. At this time, the surface reflection is very weak, however model guidance agrees on a discernable low appearing tomorrow associated with the mid level low.

A piece of the polar vortex will break off and drift westward, allowing for the mid level low to rotate across LI and into the Gulf of Maine. Strong blocking, the theme of this winter, will continue to the north, preventing the low from making much northward progress. By Tuesday morning, surface low pressure will develop steadily along the NJ coast, and drift west-northwest across Cape Cod. There is some disagreement on the exact track of the low. The internation models, ECM, CMC, and UKMET are furthest SE, while the GFS and NAM are on the west side of guidance. The main difference being precipitation type on the coast, and dry slot issues in eastern MA.

Warm air advection will trigger the start of light to moderate snow across the region late Monday night into Tuesday morning. As the mid level low continues to wrap up to our SE, cold conveyor belt banding will bring additional moderate to heavy snow for a portion of New England through Tuesday evening. Where this banding sets up will dictate who gets the jackpot.

Even the southeast side of the model guidance gives a solid hit for western and central New England. At this point, confidence is building for a jackpot of 8"+, probably across central MA into central and SE NH. The GFS agrees the least with this senario, with highest totals across eastern NY and western New England, however it should begin to shift SE tonight, in accordance with the rest of the guidance.

Preliminary forecast for Keene,NH: 4" to 7"

Back and forth

2010-02-09T22:06:00.000-05:00

Keeping an eye on water vapor imagery right now as the closed upper low is shown distinctly crossing over Kentucky. This is a little south of where models have been projecting it. The 00z model suite is coming in very similar to last nights runs, and south of the 12z/18z models. Basically, today's morning and afternoon models stranded a lot of meteorologists, including the NWS which issued a winter storm watch for 4-8" across southern New Hampshire.

Based on current satellite imagery and models, I think that even achieving 4" is unlikely.

For Keene, expect totals of 2" to 3". South of I-90, across CT and RI, totals of 8" to 14" are possible.

Timeline:
Expect light snow to develop by 10am in Keene, falling through the afternoon and tapering off by 11pm.

***It should be noted that New Englanders have not had must chance for experience in driving in wintry conditions this winter. In fact, DCers may be better than us by now. So still be cautious on the roads tomorrow.

12z runs offer hope

2010-02-09T11:41:00.000-05:00

The 12z NAM made a notable shift northwest, bringing accumulations of 10-20" into much of Massachusetts. Southern New Hampshire remains on the northern edge, where there is a tight gradient. A shift in one direction or another could mean the difference between an inch and a foot of snow. The 12z GFS also shifted northwest slightly, lending support to the overall trend. Another important signal is potential for a slower moving system. The closed 500mb low will be drifting south of New England, and the question is how much it will be able to capture and stall the surface low. Some portion of southeastern New England could see a longer duration storm Wednesday through Thursday.

At this point, the storm is within the 24 to 36hr timeframe, not leaving much room for major adjustments. The northward shift does however present the possibility of greater snows for SNH. For Keene, the best bet at this point is 3" to 6", however this is subject to change.

Another one for the Mid Atlantic

2010-02-09T08:37:00.000-05:00

We can't win, and they can't lose. The Mid Atlantic region is heading for an historic winter. Total accumulations of 10 to 20 inches can be expected from Baltimore through New York City. Extreme southern portions of New England will get in on the action as well, with 6-12 likely for Connecticut, Rhode Island, and SE Massachusetts. Further north however, accumulations in Keene will be limited to an inch or two.

Major winter storm Wednesday

2010-02-08T13:20:00.000-05:00

The Mid Atlantic region has had all the fun thus far this winter. Right now, Washington DC and surrounding areas are in the midst of cleaning up 20 to 40 inches of snow from their latest blizzard. DC is up to 45" for the season so far, while Concord, NH sits at 38".

However, places further north will get a chance to get in on the action this week. A bowling ball of energy currently dropping into the northern plains will roll through the Ohio Valley Wednesday morning. A weak southern steam system will get sucked into the mix, combining forces, triggering rapid cyclogenesis near Delmarva. The exact track of the surface low is still uncertain. It will get captured by the deep upper level disturbance, while throwing loads of Atlantic moisture back into New Jersey and southern New England. By Thursday morning, the entire system will be drifting east, ending precipitation.

The jackpot right now will likely fall over much of New Jersey and southern New England, with lighter amounts north of the Mass Pike. These areas could see upwards of 20" before all is said and done. For Keene,NH, conservative is the best way to go right now, weary of a sharp cut off to the north. 2-4" is the best bet.

Cold and dry ... and boring

2010-01-29T15:45:00.000-05:00

Despite the historic nature of this winter for much of the northern hemisphere, portions of New England, particularly the Connecticut River Valley, have remained unscathed from major snowfall. For Keene, NH, the season snow total so far sits at 38", or about near the average for this time of year. However, we have yet to see any storm accumulations eclipse 10", continuing the streak that extends back to March 2007. Much of our January total comes from an assortment of 1" snowfalls.

Now, we watch the south get hammered for a second time this season. The first storm, on December 19th, dumped a swath of 1' to 3' from Virginia to New Jersey. This current storm will be passing even further south, squashed by an intense polar vortex displaced anomalously equatorward. This storm will paint a stripe of 12+" totals from Tennessee into southern Virginia.

Meanwhile, New England is in the freezer. A wave swinging around the aforementioned polar vortex delivered some snow squalls yesterday, even featuring thunder and lightning. Behind those squalls, northwest winds kicked in, gusting over 40mph in many places, and pushing arctic air toward the coast. Daytime temperatures today were steady in the teens, and will tumble below zero tonight.

So what does the future hold in store for us? Not too much for the next week. The polar vortex will retreat northward by Wednesday allowing for moderating temperatures. A weak wave originating in the northwestern US will slide eastward, possibly triggering some light overrunning snow across SNE. Next system comes at the end of next week. A short wave sharpening as it moves across the deep south will support intensifying surface low pressure. Model guidance currently drags the low northeastward up the coast. Obviously a lot of uncertainty at this range, and considering the track record of projected coastal storms this winter, a southerly solution is definitely favored.

In the long term, it looks like the Arctic Oscillation will tumble back into the basement for a while. The Euro and GFS both develop strong ridging up into Greenland and the polar regions. An unrelenting El Nino will continue to pump a strong subtropical jet through North America. So there should be no shortage of storminess in the nation, but the question remains whether these systems continue to be suppressed southward. Long range ensembles suggest some rise in heights over the southeast (day 10 and on) as a long wave trough drops in on west coast. This may help with at least some moderate overrunning events in the northeast.

Precipitation moving north

2010-01-17T16:04:00.000-05:00

A mix of snow, sleet, and rain has overrun much of Connecticut and will be entering MA shortly. Radar echoes are starting to nudge over southern NH.

The precipitation is a bit ahead of schedule, and seeing the dry slot closing in is a little intimidating, but we will likely see the radar fill in to the south as low pressure intensifies from NJ to Long Island.

The 18z NAM and 15 SREF are robust with QPF and snow over southern NH into northern MA. The NAM spreads 1+" QPF west to I91, with an area of 1.5+" to our east. The 15z SREF has 50-60% probabilities for 8+" over SNH and even a 30-40% spot for 12+" over Hillsborough County. If not verbatim, definitely lending support to a 12 hour period of heavy snow.

Snow should be wrapping up by late morning Monday.

Snowfall forecast for Keene,NH (through Mon): 6" to 8"
for elevations >1000ft: 8" to 11"

Moisture streaming north

2010-01-17T08:59:00.000-05:00

Low pressure developing over Virginia this afternoon will move north toward Long Island later this evening and tonight, spreading Gulf of Mexico moisture over New England. High pressure will remain intact to the north all the while, funneling colder air south, and changing any rain or sleet to snow by 9pm tonight. The heaviest snow can be expected between 11pm and 4am as the H5 low crosses Long Island.

More details to come as we move into nowcast time.

Snowfall forecast for Keene,NH (Sun-Mon): 6" to 8"
For elevations above 1000ft: 8" to 10"

Potential for significant snowfall Monday

2010-01-16T09:44:00.000-05:00

6z model guidance backed off QPF by a lot, however so far the 12z runs are much wetter. Taking into consideration the origins of the storm down in the Gulf of Mexico, the wetter solutions have more support. For now the dry 6z runs are being thrown out.

Consensus building for around .8" of liquid equivalent through Monday. We've seen a notable shift to the east in recent runs of the NCEP models, while the ECM/UKMET remain further northwest. The easterly shift gives more confidence to ptype as snow, but is also starting to chip away at QPF back west.

This promises to be a dynamic storm system with good frontogenetic forcing and a period of strong omega. Some portion of central or southern New England will likely come out of this storm with 10+".

A winter storm watch has been issued for the area.

Snowfall forecast for Keene,NH (Sun-Mon): 5" to 8"
For elevations above 1000ft: 7" to 10"

Model guidance shifting north

2010-01-15T16:07:00.000-05:00

There has been an overall trend northward in the last 24 hours. The NAM in particular, which previously grazed SNH, now delivers over 1" of liquid equivalent to the area. In fact all of southern and central New England see over 1" from the NAM. Keeping in mind the NAM frequently overdoes QPF, and considering other model guidance, might trim it back to over .75" for the region.

However, with the north trend also comes warmer temperatures, so there is increased concern for mixing. To start, we do not have any antecedent cold air in place, so all our cold air support comes from the high to the north and dynamics within the storm. While this should also restrict a significant ice event, a period of freezing rain (likely south of I90) could cause light accretion. Otherwise, a mainly snow event is still expected north of the NH/MA border, with periods of sleet mixed in. For Keene, temperatures will likely be isothermal through 850mb, with a small warm layer possible near 850mb, causing a mix with sleet.

Timeline:
Model guidance is still uncertain on the timing of the storm. The GFS remains on the fast side of the guidance, moving everything through by late Sunday. The NAM on the otherhand, doesnt bring precip in until midnight. The general consensus is that this will be a Sunday night event (helping to some extent with cold air issues), with snow ending late morning Monday.

Totals:
Still lots of uncertainty and potential for changes. The consensus on the track of the 850mb low is through PA and across LI, which places maximum snow accumulations over southern and central NH. Good storm dynamics and an isothermal temperature profile should help keep precipitation mostly in the form of snow, and give us good snow growth. Still, concerns for sleet keep the forecast down from its fullest potential.

Current snowfall forecast for Keene,NH (Sun-Mon): 4" to 7"

MLK storm gaining support

2010-01-14T14:44:00.000-05:00

Model guidance has trended northward over the last few days, extending light to moderate precipitation into southern New Hampshire. The GFS has been the most robust with low pressure tracking inside the benchmark. The 12z Euro recently shifted north, in relative agreement with the GFS. The UKMET and GGEM remain on the south side of the guidance but have come north considerably in the last 24 hours.

First point to make is that this storm is primarily southern stream. One general trend we've had this season is for southern waves to gain intensity over time on the model forecasts. We'll have a large moisture supply, with origins of low pressure near the Gulf of Mexico coast.

Second, guidance is suggesting multiple interactions with the northern stream: first over the southern plains, with energy phasing into the southern wave, and second with energy dropping southeast into the Great Lakes region Sunday night into Monday. If nothing else, this second disturbance will help drive back ridging to the west, helping the southern wave develop a negative tilt and more northward trajectory.

Looking at expected liquid equivalent accumulation, southern NH remains on the fringes, but support is increasing for a general .25" to.5". Amounts increase to the south, up to 1.5" across CT into SE MA. There, however, precipitation will fall as a wintry mix.

The pattern that has developed in the last week has shoved all the cold air in the CONUS, north into Canada. New England is holding onto the remains of the cold air as an east based negative NAO is just hanging on. High pressure to our north will help reinforce cold air at the surface, but warm advection ahead of the approaching low will raise temperatures aloft above freezing. This spells trouble with ice, primarily for areas of southern MA and northern CT. For southern NH, expect a mainly snow/sleet event.

AT THIS TIME, snow accumulation forecast for Keene: 2" to 4"

Keep in mind, it's still early, and changes to the forecast are inevitable through the weekend.

A quiet pattern ahead

2010-01-05T16:51:00.000-05:00

While this winter has been relatively quiet locally, the east coast has seen a good share of storm activity. However, we should see a break from the storminess over the next couple weeks. This next event, for Friday, has not improved at all in the model guidance. The consensus remains for a strong piece of energy to drop into the northern plains, however, the mass fields are too compressed south of the wave to allow it to amplify. The wave gets sheared, and never produces a storm of any significance. We will likely see some light snow Thursday night into Friday (timing shifted earlier due to the speed of the wave).

Beyond that storm, the ridging out west is projected to break down and shift eastward, giving way to a Gulf of Alaska low. The fate of the NAO block is somewhat uncertain, but at this time it looks like the block will stand its ground. The Arctic Oscillation for sure, is showing no signs of immediate recovery from the deep end.

What are the ramifications of this pattern shift? We can expect a respite from any notable storms for a little while, and a brief period of above normal temperatures toward the end of next week.

Storm potential Friday

2010-01-03T19:00:00.000-05:00

The next storm on the horizon is progged by most model guidance for Friday (1/8). A shortwave will amplify on the east side of the west coast ridge, and dive southward out of Alberta on Wednesday. By Thursday, the position and amplitude of the wave becomes less certain, as model guidance diverges. However, there is still agreement on low pressure intensifying off the east coast on Friday. Again, models vary with regards to intensity and position, and the origins of the low. Enough cold air will be in place for snow, and decent snow to liquid ratios too. The question becomes how much moisture is available. The potential does exist for a notable snow event Friday through Friday night/Saturday morning.

A long duration storm

2010-01-01T12:22:00.000-05:00

Sun has broken out over western New England as the lead shortwave moves east of the region. Expect clouds to increase again this afternoon as the northern shortwave digs southeastward.

Water vapor imagery indicates an intense storm developing in the Gulf of Mexico. Rain and thunderstorms have overspread northern Florida in association with this system. The storm will move northeastward out into the open Atlantic this evening and strengthen slowly.

As the northern system digs, the two wave will phase, allowing for an upper low to develop and deepen just southwest of New England. The phased energy will trigger rapid strengthening of the surface low during the day Saturday. The upper level pattern will pull the surface storm system westward, back toward New England, as the surface pressure bottoms out, near 960mb in the Gulf of Maine.

The primary question is how far southwest will the surface low retrograde. The primary target for heavy snow is much of Maine, where the storm will be driving 50kt northeast winds transporting moisture in over the land. Back across western and central New England, winds will be more northerly, and not as moisture laden.

An inverted surface trough extending westward from the low will initiate enough lift to generate light to moderate snowfall across much of New England Friday Night through Sunday. Most of the region will pick up at least 4" from that alone. Further east, the wound up storm will deliver some heavier snows, where at least 6" is likely.

For the Keene area, expect 4" to 8" totals, spread out over 48 hours.

The winds may turn out to be the primary concern. A very tight pressure gradient will develop over New England, between a 960mb low, and a 1040mb high to the northwest. Gusts to 40mph are possible over western New England, with 60mph gusts possible further east.

Part one tomorrow

2009-12-30T19:01:00.000-05:00

The first chapter of a long novel of snowfall begins tomorrow. A weak shortwave will slide quickly through southern New England tomorrow afternoon and evening. Surface low pressure will approach from the south, with warm advection out ahead moving precipitation into the region from SW to NE. Temperatures will be cold enough for all snow north of I90, with rain mixing down to the coast. Precipitation will be light and snow will accumulate only an inch or two through Thursday night.

---

More details on Part two will follow later tonight.

Major snow storm Thu-Sun

2009-12-29T08:40:00.000-05:00

Confidence is growing for a long duration major snow storm for portions of New England from Thursday through Sunday.

The storm that came through yesterday that dumped a few inches of snow is associated with an elongation of the polar vortex. This huge trough will rotate into the North Atlantic, setting up a strong -NAO block.

Back west, we have a number of shortwaves to discuss that will come into play.

1) Lead shortwave in the southern stream
2) Primary shortwave in the southern stream
3) Shortwave in the northern stream

The lead shortwave comes into play first with respect to sensible weather in New England. Vorticity advection along with warm advection ahead of the northern stream shortwave will generate light precipitation across the region on Thursday. Precipitation should begin as snow, possibly mixing with sleet and rain up into northern Massachusetts as warm advection raises mid level temperatures. Any accumulation will be under 3".

The next stage begins late Thursday night with the primary southern stream shortwave. The wave will move toward the Delmarva peninsula on Friday, triggering weak cyclogenesis south of New England. Precipitation will spread north ahead of the low. Temperatures will be marginal for snow away from the coast. Coastal areas will likely see rain initially. This senario is certainly changeable. A sharper shortwave would trigger stronger cyclogenesis. This is also a function of the strength of the lead shortwave.

Friday night, the southern wave will lift northward up the coast, and the northern wave will begin to come into play. By Saturday morning, the two wave will be phasing, and developing into a closed upper low over New England. This upper low captures the surface system, and is held in place by the strong -NAO block. Model guidance has been suggesting the storm continues to affect New England potential as late as Monday. Where the low stalls will determine what areas will be under its constant influence.

At this point, the primary target area is Maine, where the stalled low may be dumping moderate to heavy snow for 2 days straight. Again, this could change. As long as the capture and stall senario remains constant however, some portion of New England could see accumulations of 2 to 4 FEET before all is said and done.

A very preliminary guess for snowfall Thu-Sun:

Quick light snowfall today

2009-12-28T10:36:00.000-05:00

A brief period of moderate to heavy snow will affect the Monadnock Region between 11am and 1pm. A vorticity maximum rotating around the polar vortex over the Hudson Bay in Canada is promoting an area of decent lift. Assisted with a conditionally unstable airmass, an area of moderate to heavy snow is progressing slowly through the Berkshires and southern Greens. Expect a quick 1 to 2 inches as this band passes over.

---

A significant snow storm is possible Thursday night through Saturday. Stay tuned.

Historic December spilling over into January

2009-12-26T13:30:00.000-05:00

An historic December is likely to spill over into the new year. While Keene has not been directly affected, you've likely heard all about the mammoth blizzard that pounded the Mid Atlantic region up into southern New England, from Washington D.C. through Boston. We've seen a number of cut off lows develop over the nation, the blizzard being one of them, assisted by a dominant convoluted flow.

The primary cause of this pattrn can be traced to a literally record breaking Arctic Oscillation. The Arctic Oscillation (AO) is a measure of blocking in the polar region. The AO is directly related to something called an annular mode which is characterized by pressure anomalies over the polar region and midlatitudes. A negative AO indicates blocking, or higher pressures near the north pole. In these instances, the polar vortex is displaced southward. The vortex disrupts the flow, making it more convoluted and favorable for storm development.

Getting back to the current situation, the AO crashed around the 10th of December, reaching a record low of -5.668SD on December 21st. Since then, the AO has remained below -4SD (off the CPC charts), and December 2009 has placed 7 days on the top 10 lowest December AO list.

The AO shows no signs of recovering through the first week of January.

What does this mean? Well, we will see no shortage of cold or storm potential. Currently, the period of January 1-3 is being highlighted by model guidance for a major to historic storm. The ECMWF in particular, has been advertising a storm moving slowly up the coast and being captured and stalled near Long Island. Verbatim: snowfall measured in feet, and blizzard conditions for days. This storm potential is about 7 days away, so there is plenty of room for changes. The GFS has lost the storm for now, however this is a common action by the model in this time range.

There is also uncertainty as to the timing of the storm. Some of the guidance develops the system earlier than the ECMWF. The differences are a result of making different shortwaves phase. This is in fact a very good sign for storm potential in my opinion: The idea that this storm may be produced in multiple ways increases the probability that it will happen.

Another killer gradient

2009-12-19T09:13:00.000-05:00

First guess for weekend snowstorm

2009-12-18T12:53:00.000-05:00

Watching this weekend closely

2009-12-17T18:33:00.000-05:00

I mentioned the threat for a snowstorm on the main page a few days ago. Things have gotten even more interesting since then. Specifically today, we've seen certain developments that are hinting at a major to historic snowfall along the eastern coast this weekend.

I don't have much time right now, as a chemistry final tomorrow morning takes precedence (yes, it's a close call I'll admit). Anyway, what we've seen for the last few days on the models is low pressure strengthening along the southeast coast and moving slowly northeastward, while delivering a one to two foot snowstorm to the portions of North Carolina up through Virginia and Maryland. However, the strong polar vortex to our north shunts the storm out to sea and leaves all of New England dry.

Today, this changed.

The 12z ECMWF came much further west, with low pressure tracking near the 40N/70W benchmark, and giving southern New England a widespread 6" to 12" snowfall with an area of 12+" in eastern Massachusetts.

The 18z NAM did a little more. By 48hrs, significant differences had developed between the 18z and 12z runs, with the polar vortex stretched out and displaced much further east. This allowed for a low pressure to creep up the coast while rapidly strengthening and literally brought blizzard conditions to all of the east coast including New England with snowfall totals of 1 to 3 FEET from North Carolina up into New York State and much of New England.

The 18z GFS was not near as robust. But at this point, we have the NAM, the ECM, and the UKMET squarely in "New England snowstorm" territory.

Tonight's model runs will be the most important runs in many years.

The potential exists for an historic snow storm for at least Washington DC and possibly extending further north.

Arctic blast, weekend storm?

2009-12-15T08:51:00.000-05:00

I don't have much time, being in between finals at the moment.

Anyway, we are looking a major arctic blast hitting the northern tier of the nation this week. A cold front sliced through the region this morning with little in the way of precipitation, however the story is what comes in behind it. Strong surface high pressure has dropped into the central Plains and will be drifting eastward through Thursday. Northwest winds will be ushering in the airmass over the northern Plains and Canada, where high temperatures stuggle just to get above zero! This airmass will modify as it reached New England, but we can still expect highs only in the teens and low 20's Wednesday through Saturday.

What's the cause of this sudden regime shift? In the last few days a mammoth block developed over the polar region, completely displacing the polar vortex south into Canada. Right now, you can see the intensity of this block as measured by the Arctic Oscillation (AO) which is currently at -3.8SD (almost off the CPC charts!).

What can we get out of this other than cold air? It's still uncertain. The potential for a storm this upcoming weekend continues to look interesting. The shortwave associated with today's frontal passage is an extention of the polar vortex, and will be closing off over New Brunswick. The evolution of this new low will be crucial to our weather this weekend.

Energy riding up and over the ridge out west will dive into the central Plains by Friday. Surface low pressure will develop in the Gulf of Mexico associated with a weak upper level shortwave and a preexisting baroclinic zone. Beyond this point, a lot of disagreement exists in the model guidance. The new Euro agrees to some extent with the GGEM and shows the central Plains shortwave picking up the surface low and intensifying it just off the east coast. The American models are less enthusiastic.

There is a lot of uncertainty, but the potential does exist for a significant to major snow storm for the northeast this weekend. A lot can change in the next 5 days, in either direction.

Watching out for icy conditions

2009-12-13T17:11:00.000-05:00

Light snow has begun to mix with sleet, freezing rain, and rain across southern New Hampshire. Surface temperatures are just below freezing, so some icy conditions can be expected through the evening. A winter weather advisory has been issued to cover this threat.

Precipitation should wrap up before midnight, however that does not eliminate all hazards. Temperatures will rise above freezing for a time around midnight, but subsequently fall into the mid 20's by morning. Wet roads will freeze, and black ice could be an issue for the morning commute.

Wintry week ahead

2009-12-13T09:27:00.000-05:00

But we won't have much to show for it. A storm developing south of the region today will move northward, in the warm sector of a storm to the northwest. Overrunning precipitation will move into New England. Despite such a chilly start to the day, temperatures will rise quickly on warm advection, allowing precipitation to fall as rain for most of southern New England this afternoon. For southwest New Hampshire, a few hours of wet snow is possible before the changeover, however, no more than an inch of accumulation is likely.

The system to the northwest is dragging a strong cold front through the Great Lakes and northern Plains. Arctic air is streaming south behind the front. A shortwave in the southwest will pick up a lee trough in Colorado, moving it along the front into the Great Lakes by Tuesday. The best lift will likely be north of the region, limiting southern New England to more showery precipitation. Again, warm advection will allow most of the precipitation to fall as rain.

Behind this storm system, the arctic front will push through, with H85 temperatures dropping down to near -20C by Wednesday afternoon. Expect high temperatures on Thursday to struggle into the low 20's.

A light snowfall likely Sunday night

2009-12-11T10:32:00.000-05:00

Currently, we have a large broad trough sitting over North America with a polar vortex over northern Saskatchewan. We have a very fast flow through the CONUS right now, limiting the potential for deepening waves. However, we will see a few flat waves sliding through over the next few days. One of interest will be ejecting eastward underneath Alaskan ridging by Saturday afternoon. Again, model guidance keeps the wave very weak -- barely discernable at all -- until maybe the Ohio Valley, and allows it to deepen a little once it reaches south of New England.

This midlevel shortwave will pick up a small surface reflection originating in the Gulf of Mexico, and pulls it northward, still as only a weak low pressure area. We will see increasing warm advection through Sunday, and precipitation start to spread northeast by Sunday afternoon. Expect mostly rain south of the Mass Pike, but north of the pike, we could see a light snow event, possibly up to 2" to 4" in southern New Hampshire.

Heavy snow reports

2009-12-09T06:05:00.000-05:00

A shield of moderate to heavy snow is impacting southern New England this morning. Reports coming in from Connecticut indicate snowfall rates over 2"/hr. Upstream observations across Pennsylvania show heavy precipitation moving in. Target time of 9am to noon still looks good for heavy snow in Keene. Count on total accumulations to be closer to the upper portion of the forecast range: 8" to 9"

Low pressure continues to deepen near Chicago; now under 984mb. 6mb/2hr pressure falls are located over Delmarva and southern New Jersey in association with the developing secondary low.

Watching the radar

2009-12-08T22:10:00.000-05:00

Radar echoes are already working in across SE New York State. Much of this is not reaching the ground, however if you go back southwest, much Pennsylvania is now getting light snow. The 00z NAM has a faster onset, coinsiding with these radar observations, and I think Keene may be seeing moderate snow by 6am Wednesday, with an inch on the ground.

Another interesting map to watch is surface pressure and pressure falls. The low now over Missouri has fallen below 992mb, and is in the process of strengthening rapidly. Again, it will likely bottom out near 970mb over the Great Lakes tomorrow! However, if you avert your attention eastward, there is a second maximum in pressure falls now over the Outer Banks of North Carolina and a distinct "bagginess" to the isobars. This is definitely a sign of our secondary taking shape.

So overall, I think we're staying on track for at least a good 6" snowfall, possibly more. Again, I want to emphasize the 9am to noon period when I think conditions are really going to deteriorate. After noon, might have to deal with a bit of icy precipitation before things wind down completely.

Snowfall forecast for Keene: 6" to 9" -- I don't see much reason for change in either direction right now.

--- Snowday Outlook ---
I'm going to hold with the current percentages, although the earlier start time that is being suggested is definitely a plus. I think the chances look good for a cancellation.

A period of heavy snow likely

2009-12-08T17:13:00.000-05:00

The 18z NAM came in even more robust with secondary low pressure near New York City assisting in the development of an area of heavy overrunning precipitation in New England. Again, the period I've been targetting looks good: In the three hour period from 9am to noon, we could see accumulations around 6" in Keene. The NAM is calling for intense omega intersecting the snow growth zone around 500mb supporting great dendritic growth and a period of high ratios, in addition to a huge delivery of moisture.

The next big question is when we can expect precipitation changes. There are too areas in the column to watch. The first is up near 700mb where an inversion may poke above freezing, and the second is in the boundary layer. The GFS warms the boundary layer faster than the NAM, switching precipitation over to rain by 1pm. Depending on how fast temperatures aloft warm, in that layer near 700mb, we could see a period of sleet and freezing rain. Again, I don't expect this to rob us of much snow, as the best moisture and forcing should be through already.

Snowfall forecast for Keene still stands at 6" to 9". Updates this evening.

--- Snowday Outlook ---
An hour earlier start to the snow would raise my confidence considerably. As it stands, snow will be falling at 530, with a coating to an inch probable before 7am. After that, conditions will deteriorate pretty quickly. I think chances for a snowday look pretty good at this point.

First call for Wednesday snowfall

2009-12-08T10:38:00.000-05:00

12z guidance has rolled in wetter. Confidence is high now for over an inch of liquid equivalent. Snow should be falling before daybreak Wednesday, with up to an inch by 7am.

Snowfall forecast for Keene, NH: 6" to 9"

Significant snowfall Wednesday

2009-12-07T20:23:00.000-05:00

The potential for a significant snowfall over 5" is improving for Wednesday. Model guidance continues to bring over an inch of liquid equivalent to most of New England. The NAM has become more robust with developing secondary low pressure south of Long Island and moving it northward over southeastern New England. This would allow colder air to be entrenched in the region longer, and as a result, greater snowfall totals. However, the strong secondary low is not a model consensus and there are definitely details to be ironed out.

Temperatures will be fairly isothermal up through 700mb starting as early as Tuesday evening as warm air advection intensifies aloft. However, the column should remain below freezing through the morning hours. This is when the bulk of the precipitation will fall anyway, so the majority of liquid equivalent should fall as snow or sleet.

The next question is the quality of snow growth. The snow growth region will be between 600mb to 450mb in the morning, shrinking to 550mb to 450mb by the early afternoon. The best omega comes right around 14z to 15z between 500mb and 400mb and continues at moderate strength through 18z, before it shuts off for the most part. We should get a decent thump of snow between 14z and 17z. By 18z, count on a change to sleet, maybe some freezing rain, and light rain later in the evening. Showery precipitation may continue behind the storm through Wednesday night, and should change to snow as cold air advection work in after midnight.

Current thoughts on total snow and sleet accumulations in Keene: 4" to 7"

--- Snowday Outlook ---
First real threat of the season is coming up Wednesday. Snow should start to fall by 6am Wednesday morning, and fall heavily between 9am and noon, accumulating to between 4" and 7". By 11am, precipitation will begin to mix and change to sleet and freezing rain, and by 1pm, plain rain. I think the moderate snow accumulations in the morning plus ice potential may be enough for a cancellation, however I'd like to be more confident on higher snow accumulations, and a slightly earlier start time.

Overview of this week's storm

2009-12-06T21:40:00.000-05:00

More details later. A snow and ice event looks likely for central New England on Wednesday.

Quick intro to Wednesday's storm

2009-12-05T23:48:00.000-05:00

I don't have much time right now, and will have even less tomorrow, but I wanted to give a quick introduction to our storm threat next week.

It all starts with a trough amplifying over the Pacific northwest through Monday. By Tuesday, that energy drops into the southwest, and triggers surface cyclogenesis over Colorado. The trough will move through the southern plains, tilting negative Tuesday night into Wednesday, with strong low pressure moving into the Ohio Valley.

A couple things model guidance is starting to latch onto is that this primary low will move west of New England, and likely will be at least down into the 980's if not lower (UKMET run had a 966mb low yesterday).

The next variable is with the development of a secondary low off the coast. Timing and location are incredibly important. The faster this secondary gets going, the better our chances for snow. As it is, this should deliver a decent front end snowfall, with warm air overrunning cold air at the surface and moderate to heavy precipitation spreading northward. We could be talking about 1" to 3" of water equivalent associated with this system. With not much antecedent cold in place, ice should not be a huge issue (as in last December), although a period of freezing rain in a transition from snow to rain is possible, with moderate ice accretion.

So in general, an intense storm is in store for the eastern half of the nation, but many details need to be ironed out. Stay tuned.

Banding delivers

2009-12-05T16:35:00.000-05:00

You can see on radar a nice band extending from Albany to Keene through Plymouth,NH that has been dumping moderate snow for a few hours now. Reports from Keene indicate a half to inch and half of accumulation so far, and some of the best rates are still on the way. The RUC has been persistent in developing a band of moderate to heavy snow through interior southern New England, propagating eastward this evening. Specifically, between 530pm and 8pm, snow may fall heavy at times in Keene. Snow will wind down past midnight tonight. Count on total accumulations around 3" and up to 5" in the higher terrain.

Nowcasting

2009-12-05T11:00:00.000-05:00

Radar trends continue to look good, with a large region of precip extending from Virginia up through New York and Massachusetts. Reports out of western MA indicate precipitation is starting as a rain/snow mix, so I'd expect the same north of the MA/NH border as things start up later this afternoon. Low pressure is consolidating just off the Outer Banks of North Carolina right now. Great upper level dynamics in place for steady intensification tonight and periods of heavy snow across central and eastern MA. NWS still keeping advisories south of the MA/NH border, but I think they will have to change this for sure, and possibly put out a warning for a part of Worcester and Middlesex counties

---
Apparently, still having some technical issues, probably related to a new application I'm test driving. Anyway please forgive some of the editting on the last post; the Keene forecast numbers were very old. The map is current.

So to clarify, Keene snowfall forecast: 2" to 3.5"

First and final map

2009-12-05T08:47:00.000-05:00

I was actually meaning to have this up last night, but I had some technical difficulties. Anyway, moderate snowfall still looks likely for southern New England. Model guidance has backed off QPF to some extent to the northwest, which is a common adjustment in fact. We may be looking at a fairly sharp cutoff to accumulations. However, Keene should be able to rack up a couple inches tonight. GFS is still east of the NAM, however general consensus brings the low just outside the benchmark. NAM continues to deepen low pressure more than any other guidance east of Cape Cod, and I think we could see a decent band set up with the cold conveyor belt in eastern Massachusetts later tonight. This is where I am expecting maximum totals on the order of 4 to 7 inches.

Rain on radar has spread across southern New England this morning, although much of this is virga for the time being. As the column saturates, light rain will develop and fall through the afternoon. The interior should start to see some flakes mixing in by 3pm, and Keene should be over to all snow by 5pm.

The NWS in Taunton has issued winter weather advisories for all of MA, northern CT, and RI, away from the coast. I think they may have to expand at least into eastern Hillsborough in later shifts.

Final call for Keene: 2" to 3.5"

---
A major storm is becoming more likely for the middle of next week. I will post more details later today. Stay tuned!

Storm west and stronger

2009-12-04T15:37:00.000-05:00

A moderate snow storm for portions of New England appears likely now for Saturday Night. The 00z Euro and 06z GFS came notably west and are conforming to the NAM solution. Per model consensus, a widespread 3" to 6" is likely for southern New England up through eastern New Hampshire and southern Maine. The main differences involved are the position and amplitude of the southern shortwave. The NAM in particular, actually continues to trend toward a stronger wave, and the latest 18z run deepens the surface low into the mid 980's east of Cape Cod.

A lot of things to consider when developing a snowfall forecast for this storm. Boundary layer temperatures will be an issue during the day Saturday for most of southern New England but will be confined to the coastal plain by the evening hours. Dynamic and diurnal cooling overnight will help coastal areas turn to all snow as well. Total QPF is looking on order of .3" to .5" for western and central New England, increasing to .6" to .9" near I95. We'll likely see enhancement just north and west of I95 with the cold conveyor belt. Maximum snowfall in these areas will probably run between 5" and 8".

For Keene, QPF will be the main issue on the western edge of the precipitation shield. Good consensus forming for at least .25" w.e. so the Monadnock region should definitely see accumulations over an inch. Best guess at this point is 1" to 3".

I hope to have a forecast map out in a few hours.

Model disarray

2009-12-03T20:18:00.000-05:00

We can say with confidence that low pressure will eject from the Gulf of Mexico on Saturday and move northeast through Saturday night. However, beyond that, there is a lot of confusion as to the ultimate track of the low.

The GFS has been adament on sending the low well southeast of the region, keeping everyone, except maybe the cape, precipitation free. The Euro has been consistently a little west of the GFS, but still well offshore, and a miss for New England. The NAM has been west, and in the 18z run, dumps 3 to 6 inches over much of the region. The UKMET is also west, but not as extreme.

At this point, a GFS/NAM compromise is looking good -- something close or just west of the Euro. Tonight's 00z runs will be very important.

As colder air drains in behind this latest storm, and is reinforced northwest of the weekend low, precipitation could fall as snow as far south as Louisiana. In fact, there are winter storm watches out down there, and for the mountains in western North Carolina. Yes, it is possible that these southern locations rack up seasonal snow totals before Keene, NH does.

---
Beyond this storm, there is a growing threat for a major system affecting the eastern third of the nation next Wednesday into Thursday. I hope to post more details tomorrow night.

Watching the weekend

2009-12-02T17:12:00.000-05:00

You may have already heard some whispering about a possible nor'easter this weekend. I've been watching the models carefully over the last week as they bounce around with forecasts ranging from a big New England snow storm to a track well offshore. At this point, all model guidance is delivering only a glancing blow to the region.

There are a number of factors in the mix that have to be right for a direct hit. First we have issues out west as a trough drops in the Pacific northwest Friday and Saturday. In southern Canada, multiple shortwaves will be rotating around a large upper low. One of them will be the source for our storm this weekend. A wave behind it will make things complicated as it may phase with the energy in the northwest US, allowing for faster zonal flow across the nation. In turn, the first wave is suppressed to the south.

A second factor involved is how much phasing can occur between our southern wave and energy up in the Great Lakes. The more, the better, for pulling this storm further north.

At the moment, all models keep interior New England dry, but there has been slight trending west with the coastal low over the last 24 hours. The NAM is currently the most robust with delivering a moderate snow storm to the region. Certainly bears watching, but I'm not getting my hopes up.

Back in business... soon?

2009-11-29T15:50:00.000-05:00

I've been away from the site for quite some time, aside from periodic posts of GFS fantasy storms. As it is, Keene saw its first flakes back in October, but has yet to see accumulating snows. Neither has much of northern New England for that matter. You in fact have to head south to find numbers up on the seasonal snowfall scoreboard. The couple of October events delivered a few inches to parts of Massachusetts and even Connecticut.

Now we are about to enter the time of year when climatology is a little more friendly to snow-lovers. Meteorological winter begins on Tuesday!

But when will true wintry weather actually make an appearance? Chillier temperatures are in the near future. With a frontal passage on Monday, the middle of the week should feature temperatures closer to the seasonal normals; in the low 40's during the day and the mid 20's at night.

However, the prospect of snow is still bleak. In the short term, a strong piece of energy in the southwest will eject east into Texas on Wednesday with surface cyclogenesis on the Gulf Coast. This low is expected to move north into the Ohio Valley on Thursday, spreading moderate to heavy precipitation into the region. While the track is of course uncertain, the expected senario is for New England to be in the warm sector, keeping precipitation in the form of rain and this storm out of the winter weather discussion.

Further out, there are a number of factors pointing toward a period of below normal temperatures in the east. In the Pacific, the MJO wave has remained strong into octant 6, with convection now approaching the dateline where SST anomalies are spiking above 2C. The ramification of this MJO wave is forcing a trough over the Aleutians and strong ridging over Alaska, which is in agreement with current model guidance. In addition, GFS ensembles are indicating a negative NAO developing and persisting through the next couple weeks. So we have the basic recipe for cold, and snow potential. Target time right now is between the 8th and 14th for some sort of wintry event.

The perfect storm on the 12z GFS

2009-11-07T16:29:00.000-05:00

Not going to happen, but I want to tell you about the 12z GFS forecast for midweek. It is quite interesting.

A mid level short wave trough over the Great Lakes digs south on Tuesday, and closes off over Pennsylvania Wednesday morning. At the surface, low pressure develops off the New Jersey coast and deepens rapidly on Wednesday. Moisture from the remnants of Ida gets pulled northward into the system. It is raining steadily over all of southern and central New England by Wednesday afternoon. As mid level heights continue to crash with the deepening storm, the column cools signficantly, allowing for a change to heavy snow. The storm is cut off from the flow, and sits east of Cape Cod through Thursday morning. In summary, the regions gets over 12 hours straight of blinding heavy snows with winds exceeding hurricane force!!! The GFS advertises QPF of 3" to 4" over central New England through Thursday.

Anyway, this one will be filed away in the folder marked "Twilight Zone Forecasts." In the mean time, the rest of the globals in addition to the GFS ensembles are much less supportive of Armageddon this week. They keep the shortwave over the Great Lakes more progressive and lower amplitude.

A wild storm possible tomorrow

2009-10-17T22:01:00.000-04:00

Okay, the temperatures outside are closer to November standards and the storms showing up on the forecast models are closer to December standards. One more in store, then we'll be returning to more seasonable weather.

This one looks quite interesting. It has been monitored for some time now as the last shortwave cycling through the trough over the east as it closes up and lifts northeast. We are looking at a double barreled low moving up the coast toward the region. This poses so many questions especially considering the time of year.

First, the track of this storm is still very much in question. The GFS has been fairly locked on bringing low pressure well north, while the NAM has been back and forth and the ECM has for the most part been south. High pressure to the north will be filtering in colder and drier air. This will help produce precipitation in the form of snow, however also create a tight cutoff to in precipitation to the north.

For precipitation type, chances for snow look good across the high terrain of New England, and even lower terrain north of Rt 2. There is good support for the development of banding somewhere over interior SNE. Where this sets up, strong omega with a marginal temperature profile may generate a few hours of moderate to heavy snow, that may accumulation several inches before all is said and done.

There is so much uncertainty. I have prepared a forecast snowfall map, but am cautious about posting anything definitive yet. At this point all I will say is that the Monadnock region could see accumulating snows tomorrow and maybe a suprise or two.

Storm scooting south

2009-10-15T17:27:00.000-04:00

Model forecasts are pretty locked now on low pressure passing south of the region, with high pressure keeping precipitation confined to southern New England. Southern New Hampshire will near the edge, with light QPF expected through Friday afternoon. Current radar imagery shows a large region of moderate precipitation, and in the form of snow across northern Pennsylvania into interior southern New England. Minor accumulations on the order of 1 to 3 inches can be expected in the higher elevations of northern CT and southern Massachusetts. Further north, QPF drops off quickly, although snow should reach Keene late tonight and fall through the morning hours Friday. Little if any accumulation is expected.

Of notable interest are the developments in northern PA where an inverted trough is supporting the moderate snow there. Ratios are an incredible 3:1 (very heavy stuff!) and they can expect accumulations ranging from 4 inches to 10 inches in the higher terrain. Widespread downed trees and power lines can be expected.

Looking ahead a few days, the longwave trough that has been causing all this cold weather and snow potential will be sharpening and closing off near the mid Atlantic region. Cyclogenesis off the Carolina coast can be expected on Saturday, and low pressure will move northward Saturday night, however there is a lot of uncertainty again on the northward extent of precipitation. Another chance of snow exists though.

This trough will be lifting out of the picture by next week with moderating temperatures and drier conditions moving in.

Friday continues to look interesting

2009-10-14T10:16:00.000-04:00

Tuesday morning, I gazed out the classroom window at fat white flakes tumbling through the air. There was no accumulation, but the feeling of winter was overwhelming. I am mentioning this mainly because the sensation of tracking a potential significant snow-producing storm for this Friday ... is equally as overwhelming.

There continues to be a lot of uncertainty with this forecast however. At this point, I wouldn't say things are looking promising for snowfall in southern New Hampshire, however we've seen a lot of shifting going on, and that will continue to occur... one way or another.

The operational models, GFS and NAM, continue to display a classic case of disorganized energy, with multiple packets of vorticity cancelling each other, and resulting in a weaker system.

The forecast is for low pressure originating in the southeastern US to move off the Carolina coast Thursday evening and to track southeast of the 40/70 benchmark on Friday. Precipitation spreads across southern New England however strong high pressure to the north will create a sharp cutoff, leaving areas of northern New England dry. The high pressure will also serve to drain cold air down into the region, supporting wintry precipitation.

The main thing that we want to see for snow in southern New Hampshire is energy to become more consolidated with a stronger low at the surface. This would spread precipitation further north and at the same time support cold air drainage. We see this in the GFS ensemble runs, as well as the 06z operational run, although it has not been supported by the following 12z run. The 9z SREF is also promising. Verbatim some of these solutions bring a 3" to 6" inch tree-snapping snowfall to southern NH, VT and western MA. In addition, if model guidance starts leaning this way, we might need to actually talk snowday potential Friday.... we'll see. It's October, so climatology is saying "not in your wildest dreams". Everything needs to be right to get an October snow. We've seen a gradual north trend which I think will continue, but to what extent is the question.

First forecast maps later today if models warrant it.

Tricky forecast for end of week

2009-10-12T13:14:00.000-04:00

Briefly, to start, model guidance has cut back QPF for tonight into tomorrow, still with a wide expanse of .5"+. The main effect in this case is further north where accumulation becomes a concern. The potential for trace+ will be mainly in the higher elevations north of a line from Lebanon to Laconia, NH. Some wet snow flakes could mix in down into SW NH.

The next system to discuss is much more complicated and also has more potential. The ECM has been fairly adament about developing low pressure in Texas and moving it off the Carolina coast toward New England on Friday. The GFS has been less steady. There are three separate pieces of energy to consider. The first wave remains weak and scoots out to sea on Thursday, however depending on how fast and amplified it becomes, it may have an effect on the following waves. The second wave is prefered for further development, however the third wave may interfere and that is where the GFS has been tripping. If the third wave, closely following its neighbor, intensifies, it basically causes a cancelling effect ultimately weakening both systems.

The ECM strengthens wave #2, and rotates the energy northward, east of New England. At the surface, low pressure strengthens near the 40/70 benchmark, drawing cold air south and producing inland snows. The potential continues for a notable early season snowfall for central and northern New England, however there is a lot that needs to be ironed out.

Snow Monday Night - Tuesday

2009-10-11T18:05:00.000-04:00

A short wave trough over central Montana is visible on the current water vapor imagery. This wave will traverse the northern tier of the nation tomorrow in fast zonal flow, reaching the Great Lakes region Monday night. At the surface, strong cold high pressure will be entrenched over New England. An inverted trough will move over the Ohio Valley Monday evening, with low pressure forming near Long Island Tuesday morning. Vorticity advection and warm and moist air advection from the south will encourage lift and the intensification of an area of moderate precipitation mainly north of the Mass pike early Tuesday morning. Model guidance has been fairly robust with QPF, showing a large region of >.5".

Forecast soundings are nearly isothermal up through 750mb near 0C. The main concern is boundary layer temperatures. At this point 1000-850mb thicknesses are marginal for snow around 12z (8am) Tuesday. Considering possibly a weak elevated warm layer, we could deal with a brief period of sleet or freezing rain too.

Model guidance has been trending south overall with this system in the last few day. At this time no wintry accumulations are expected in Cheshire County. Further north and in higher elevations, some first light accumulations of the season can be expected.

A significant coastal storm remains possible for Friday-Saturday. The potential exists for first accumulations of the season in southern NH and heavier snowfalls further north. More details will be posted tomorrow. Stay tuned!

More wintry potential next week

2009-10-10T17:51:00.000-04:00

The storm system scooting through on Tuesday will likely be low amplitude, fast moving, and ride the Canadian border in zonal flow. However, model guidance continues to advertise marginal criteria for snow mixing in down into northwest Massachusetts. No accumulation is expected, but up to an inch in the high elevations further north.

Believe it or not we have another potential storm to discuss for late next week. The GFS and ECM are on board with low pressure ejecting out of Texas on Thursday and moving to the Carolina coast by late Friday. This storm coincides with a negative AO and NAO and rising PNA in the west. The GFS ensembles bring the low up toward the Great Lakes. The ECM brings low pressure near the Cape Saturday morning. Both senarios would still likely drop accumulating snows on the front end of the storm. The main difference between the two is the magnitude of ridging out west and how much the -EPO breaks down. The operational GFS is a little different altogether as it develops a lead short wave that affects New England Thursday night. This is more unlikely though and the second wave should become predominant in the next few days of runs.

Anyway, some interesting bits to keep an eye on this week. Even first flakes would be fairly early, let alone accumulating snows. It's six days away and it's October, so Murphy's Law should be kept in mind.

Spring training for models

2009-10-09T10:54:00.000-04:00

The current situation across the globe is not model friendly. Certain developments in the tropics such as a brief stint for the MJO wave, and uncertainty with a propogating westerly wind burst are playing havoc with the long term model projections.

Short term forecasts are suffering a bit as well. The ECM and GFS recently shifted toward a more zonal regime for early next week, compared to the blast of cold air that had been suggested previously. The consequence of this flow is that the energy responsible for storm potential Monday - Tuesday next week will be unable to dig south much, and rather will ride across New England, keeping cold air locked further north.

Overall, the potential still exists for some first flakes in portions of central New Hampshire and the mountains into southern Vermont. Otherwise, a period of light rain showers can be expected for interior southern New England.

Snow potential early next week

2009-10-07T12:26:00.000-04:00

Model guidance continues to support the idea of low pressure deepening near Cape Cod around Columbus Day. The GFS has been particularly robust with crashing heights over New England and the establishment of marginal criteria for snow in central and northern New England and potential for significant accumulations. Obviously, the higher elevations have the best chances.

The ECM has also been on this bandwagon. The 00z run takes the low a little further south, and consequently also brings colder air further south. Track nuances are far from being locked down. This potential storm is still around day 6 so there is much opportunity for changes. However, model agreement for a storm in this period is good. Given a supply of cold air, the chances for at least some first flakes as far south as the higher terrain of Massachusetts is looking good as well.

Winter approaches

2009-10-04T12:50:00.000-04:00

Yes it's only the start of October, but I can tell you that seeing snow showers over the mountains in northern New Hampshire certainly gives a feeling of anticipation.

The month has gotten off to very chilly start across the entire nation. From the Rockie Mountains to New England, temperature anomalies are in the -5 to -10F range and lower. In fact southern Texas is the only area that has positive anomalies for the last three days.

We should see a respite from the cold this week, however the long range model guidance has been adament in delivering an early season blast of frigid air days 8-10. The two primary models, the GFS and ECM, develop above normal heights over the arctic while at the same time dropping a major trough into the eastern half of the conus. Verbatim, records could be threatened.

In addition, the model continue to show a storm system passing near New England around Columbus Day. With such a cold air mass over the eastern US and a still very warm Gulf Stream, a strong baroclinic zone develops along the coast. This could promote a significant deep storm tracking up the eastern seaboard. This is all speculation based on long range models that are sure to shift around over the next week, however given these circumstances, portions of interior New England could see an early appearance of some snow.

Preliminary Winter Outlook posted

2009-09-19T16:59:00.000-04:00

The KeeneWeather.com preliminary 2009-10 winter outlook has been posted on the main page.

Click here for full details!

PRELIMINARY 2009-10 WINTER OUTLOOK

2009-09-15T21:56:00.000-04:00

Summer Analogs:

The summer of 2009 had a number of distinct features including height anomalies associated with a predominantly negative NAO and AO while an El Nino built in the equatorial Pacific. The top analogs for the observed H5 pattern were 1950, 1951, 1958, 1960, 1965, 1977, 1982, 1985, 1998, and 2004. Filtering for the prefered ENSO conditions (details below), the list is condensed to 1951, 1958, 1965, 1977, 1982, and 2004.

Pacific:

Between April and June, SSTs in the equatorial Pacific warmed rapidly triggering a lot of "strong" El Nino talk. However, in late June, trade winds strengthened over the eastern Pacific, subduing the high SST anomalies. There have been multiple west wind pushes west of the dateline, but propogation into the western hemisphere has been minimal.

So what we've seen is a stall in the warming of the EPAC while central Pacific SSTs have been on the increase. At the start of September, the highest totals were located between 160E and 180. SST anomalies have the greatest effect in the western Pacific where totals are the highest and the exponential relationship between saturation vapor pressure and temperature dictates that evaporation rates are increased significantly with small deviations in SST. The west-based versus east-based argument matters with respect to where forcing is positioned, so even though SST anomalies may be slightly higher at times in the east Pacific, their effects are not as great and the anomalies near the dateline will have much more significance. Overall, I expect this El Nino episode to at least remain within the moderate threshold.

The convergence of the trade wind anomalies with the westerly wind bursts has provided focus for tropical convection, and we have seen this summer a number of OLR minimas just west of the dateline. Also, it should be noted that the summer analog composites display this well too.

In the north Pacific, there has been notable cooling near and south of the Aleutians. The -PDO has weakened to it's highest state since September 2007. However, at the same time, SST anomalies have cooled in the Gulf of Alaska. This has influence over the location of a trough over the north Pacific. It is clear that the north Pacific pattern will be a crucial battle ground this winter.

Atlantic:

SST anomalies in the north Atlantic have been tilted squarely toward a winter +NAO configuration. Using a regression with the two regions of interest yields a DJF NAO of +.85. However, the equatorial Atlantic is looking more favorable. There has been a general cooling of waters between Africa and South America. This should have overall weakening effect of the Atlantic hadley.

In addition, with primary tropical forcing occurring near the dateline, and some weaker forcing through the eastern Pacific, this forces an equatorial cell with sinking air over South America which again, weakens the Atlantic Hadley, and assists in the development of a -NAO.

Stratosphere:

Stratospheric easterly wind anomalies continue to make their descent, and the QBO took a steep dive this summer. Easterlies will continue to descend this winter, and the QBO will likely bottom out sometime in the spring. The descending, negative phase along with a warm ENSO period is highly supportive of a weakened polar vortex.

Preliminary Outlook:

There are definitely inconsistencies between each analog. I do not intend on using them directly, rather just as guidance for the outlook. Overall, there is a decent consensus for a dominant +NAO in December, a transition phase in January, and a dominant -NAO from late January through February. January and February could certainly feature a couple major winter storms in the eastern US. One significant x-factor is the North Pacific pattern. I think we will see the PDO become more neutral toward the winter, but another question is what happens with SSTs in the Gulf of Alaska.

Beautiful weather to continue

2009-09-06T20:18:00.000-04:00

The streak of sunny dry days will continue this week. Strong high pressure over the region and northward will suppress disturbances to the south. Daytime highs will reach the 70's with lows in the 40's to low 50's.

I have been away from the site for a little while with college starting, but I hope to continue a steady stream of updates (as the weather warrants).

To start, I have been working on my winter 2009-10 seasonal outlook which I hope to post by September 15th.

Heating up Monday

2009-08-09T10:32:00.000-04:00

A tight thermal ribbon to our southeast with warm air advection aloft is contributing to overcast skies and scattered showers over portions of the northeast this morning. Most shower activity is dissapating at this time, and most of the afternoon will likely be dry. Cloudiness will prevent high temperatures from getting out of the 70's. Overnight, The surface warm front boundary approaches with strong warm air advection and moisture advection. Lows should not drop much further than the mid 60's. We could see a round of thunderstorms move from the WNW toward the region with gusty winds and heavy rainfall possible.

On Monday, the ridge axis will slide to the east coast sending 850mb temperatures to around 18 to 20C supporting highs in the upper 80's and 90's across the northeast. In addition, dew points will reach the low 70's yielding heat indeces near 100 in some areas.

The second concern Monday is the potential for severe thunderstorm activity later in the evening. We should remain capped most of the day, which will allow partly to mostly sunny skies. By the late afternoon however, the cap may break giving way to rapidly growing thunderheads. Current severe parameter projections give support to >1" hail and >70mph gust potential. Certainly something to keep an eye on for the next 36 hours. Monday night, a true uncomfortable summer night with lows in the upper 60's to around 70 and saturated low levels.

The last shortwave arrives Tuesday, with one last day of warm and muggy weather. Expect highs to reach the mid 80's. Cold front approaches in the afternoon trigging another round of thunderstorms through the evening hours.

Wednesday through Friday look dry at this time with high pressure moving in from the west. Temperatures will be around seasonal normals. Beyond this point, the forecast becomes more uncertain. There are some signs pointing toward another period of above normal temperatures. Both the GFS and ECM push ridging into the Ohio Valley, but its ability to make it further east is the question.

Weekend Warmup

2009-08-03T20:15:00.000-04:00

High pressure will remain in control of the region through tomorrow. Sunny skies should quickly burn off patchy morning fog, and we'll recover from morning lows in the 50's to highs reaching the upper 80's. Diurnal cumulus will likely develop through the afternoon. Upper level jet remains well to our north so we should stay dry.

The next storm system will be approaching overnight with surface low pressure located up in northern Quebec and a cold front hanging down across the Great Lakes. Model guidance indicates that instability parameters will remain favorable overnight and with increasing forcing there is a slight chance for a nocturnal thunderstorm complex to cut through western New England. On Wednesday, the cold front will be slowing up with flow becoming parallel to the boundary. As daytime heating contributes to instability, we may see a second round of storms in the early afternoon. The main potential for any severe weather will be to our east though with more favorable dynamics.

Once the front pulls through, a tight temperature gradient sinks to our south. Much cooler and drier air will arrive on Thursday. Expect mostly sunny skies through the early afternoon, however temperatures will struggle into the upper 70's. A shortwave will be swinging north of the region during the evening and overnight. This will likely add some cloudiness and a slight risk for a shower.

More of the same on Friday. Upper low to our north will be rotating eastward with surface high pressure sliding into the eastern Great Lakes. Expect sunny skies but highs only reaching the mid 70's. Overnight lows will tumble into the low 50's.

Some questions arise on Saturday as there is disagreement in model guidance on the evolution of a system developing along the baroclinic zone to our south. The ECM keeps the disturbance weak and our area dry while the GFS develops a stronger low and in fact shows a very wet day for southern New England. At this point I have kept the forecast dry for Keene, NH with the expectation of any rain being kept to our south.

Weather on Sunday could be starkly different from Saturday. Strong ridging to our southwest will be expanding eastward. This will push the tight temperature gradient through New England. The exact timing of this change will dictate high temperatures. The day will likely be dry, but temperatures could top out more than 10 degrees warmer than Saturday (in the 80's, maybe 90).

The lifespan of the heat is in question however as disturbances moving through could suppress the core of the heat southward by midweek. Expect periodic thunderstorms Monday through Wednesday in this summertime pattern.

Chilly end to the week

2009-08-02T19:42:00.000-04:00

Frontal boundary crossing the region tonight will usher in drier air aloft allowing for sunny skies tomorrow. This will help highs into the low 80's. The frontal boundary will stall to our east through the evening, which may provide a focus for isolated showers over eastern MA/CT.

The next system will be swinging into the Great Lakes on Tuesday. We'll see winds backing to the southwest and a return of a more unstable airmass. A weak midlevel shortwave will trigger scattered showers and thunderstorms into the evening hours. Warmer air will be advecting into the region through the afternoon, boosting highs into the upper 80's.

The associated cold front will be moving into New England Tuesday night. Flow becomes parallel to the front into Wednesday resulting in it moving very slowly through the region. With moderate instability parameters scattered showers and thunderstorms will continue along the front through Wednesday. Highs should reach the low 80's despite increased cloud cover and cooler air advecting in later in the day.

As the front slides south of New England on Thursday, cooler and much drier air will move in with high pressure over the Great Lakes. We'll still be under the influence of an advancing shortwave which will prevent complete clearing, but we'll at least remain dry. Despite sunshine, highs will struggle into mid 70's, against northwest flow.

Friday, dry air continues to take command and with the shortwave trough departing, we should see full clearing. However, once again highs struggle into the 70's and overnight lows will tumble into the low 50's. Indeed it will feel like the beginning of autumn (not that we're not used to that this summer).

Low pressure will slide south of the region on Saturday along a baroclinic zone where the previous frontal boundary faded. This will spread some clouds into the area, but areas north of I90 should remain dry. South of I90, there will be a chance for showers. Highs again on the cool side.

On Sunday, a new chapter begins. Ridging over the southern plains will be pushing east. Remember the mentioned baroclinic zone? That's where there is a tight temperature gradient present. The developing ridging will be pushing that gradient northward. Surface high pressure slides to our east and southwest flow will blast the region with warmth. There are signs that this could in fact open the doors to heat we havent seen yet this summer. However, a number of factors also oppose that idea. First, the ground is very very moist in the northeast. In the summer months, this has a significant bearing on the potential of a heat wave. Second, an anomalous low in Canada will be spitting shortwaves southeast toward New England which will constantly suppress the core of the heat to the south. So overall it is more likely that New England sees a sharp but quick warm up early next week.

Beautiful start to the weekend

2009-07-31T20:56:00.000-04:00

Cold front will be departing tonight with high pressure building in from the west tomorrow. The mid level should dry out nicely with plenty of sunshine, however low level humidity will still hang strong especially with how soaked the ground is now. Highs should make the low to mid 80's.

Next system approaches on Sunday, with a cold front crossing the Great Lakes Saturday night and positioned over New York state Sunday afternoon. This will provide a focus for showers and thunderstorms. High low level dew points and sufficient morning surface heating will promote scattered strong cells with potential for more heavy rainfall.

The front will clear the region by Monday morning with decreasing clouds and another rebound in temperatures.

Tuesday will start out with partly cloudy skies with decent surface heating bringing us into the 80's again. Another short wave will drop into the Great Lakes Tuesday morning with associated frontal boundary moving into New York in the afternoon. This will spark another round of showers and storms through the evening and overnight.

The same frontal boundary will stall to the south of the area through Thursday. While weak high pressure builds to our southwest, there will remain a focus for scattered afternoon showers and thunderstorms. Weak waves will carve out a trough over the northeast with cooler air diving south out of Canada.

By Friday, this trough will be shifting to our east with rising heights through the weekend. Model guidance is slowly reaching a level of consensus on a closed low over the eastern Pacific sliding ashore, pushing ridging into the central plains. This ridging may expand briefly into the northeast US sometime early the following week, bringing a quick warm up to the region.

The big picture heading into August

2009-07-30T09:44:00.000-04:00

This past week has featured the most summer-like weather we've seen since April. And yet, the heat wave of late April still boasts the highest temperatures for the year in many locations. The shift west in Atlantic ridging developed a strong southerly flow over the eastern US which in addition to warmer temperatures, also transported copious moisture northward. What was already a wet month in the northeast has reached record levels after multiple rounds of tropical rains swept through the area.

Looking ahead over the next 10 days, here are some of the highlights:
(An updated official forecast will be posted tomorrow)

Frontal system moves eastward with strong upper level dynamic and moisture, producing more heavy showers and thunderstorms Friday.

Saturday through Sunday morning, the atmosphere stabilizes with sunny skies across interior New England. Highs will reach the mid 80's both days.

The next system approaches on Sunday with another round of showers and thunderstorms Sunday night into Monday.

The weather dries on Tuesday followed by a frontal boundary bringing showers Tuesday night and then drying again Wednesday with another round of showers Thursday afternoon. The general trend of temperatures will be downward through the period. Generally, looking at highs in the upper 70's to near 80 next week.

Ridging will be developing in the center of the nation next week, and will expand eastward for the weekend. The highest heat will be suppressed southward with weak disturbances riding through the northern US, however we could see a day or two with highs 5 to 10 degrees above normal.

This brings up the next point: Normal temperatures have turned the corner and are on the decline. Looking at the big picture, winter is coming up quick.

First autumn comes, and with that, increased hurricane activity. It is July 30th now, and the Atlantic has yet to see its first named storm. Activity in the Atlantic basin continues to be very quiet and no development is expected in the short term. I'll post a more detailed long term discussion and hurricane statistics in the tropical weather outlook later in the week.

The situation in the Pacific continues to be somewhat uncertain for the upcoming boreal winter. June featured a significant warming east of the dateline with weekly Nino3 anomalies reaching +1C by June 24 and Nino3.4 at +0.9. Since then, SST anomalies have held steady. However, trade winds have strengthened through July and have notably dampened anomalies. The warmest waters are currently between 160E and 180 with totals around 29.5C. The strongest anomalies remain between 120W and 130W, just west of the influence of the Chilean current. But increasing easterlies will likely begin to chip away at these anomalies over the next few weeks. Further west, a strong westerly wind burst has developed near 150E. This argues for increasing totals propogating eastward in the next couple weeks and rising anomalies in the west Nino regions. In general, through the end of August expect the development of a west-based El Nino. Whether the configuration lasts through the autumn and into the winter is the big question.

As I've mentioned in a few discussions on here over the last few months, signs for the upcoming winter (including the developments in the Pacific and a rapid tumble in the QBO) are pointing toward overall below normal temperatures and above normal snowfall in the northeastern US. More details will be added on through the autumn and of course in my winter seasonal outlook coming later in September/October.

Increasing warmth and humidity

2009-07-18T10:31:00.000-04:00

High pressure nosing in from the southwest will keep the weekend dry. Skies started out cloudy this morning, but we should see gradual clearing through the afternoon. This will help high temperatures into the low 80's. On Sunday, drier air will be advecting westward, contributing to mostly sunny skies.

Model guidance continues to support a shift in the overall pattern with ridging building over the west Atlantic and the mean trough axis shifting into the Great Lakes regions. This will develop a strong baroclinic zone along the east coast helping moisture transport into the region. With weak shortwaves riding northeast through the week, rounds of showers and thunderstorms, locally heavy, will be common across New England. Expect highs generally around 80 and lows in the low 60's.

Atlantic ridging takes a brief break Friday and Saturday with an upper low moving north of New England. That low will then lift toward Greenland, forcing a rising NAO with a resurgence of the ridge to the south. A near tropical airmass will be transported into the region early next week on southerly flow. Count on a threat for thunderstorms each afternoon. Highs in the 80's, possibly touching 90 on Monday.

Sunny and warmer Wednesday

2009-07-13T20:33:00.000-04:00

Overall, we will see increasing temperatures through the next week along with an increasing dew points. Despite sunny skies the last few days, anomalously cold air aloft has limited high temperatures over the region. Clear skies have also allowed for notable radiational cooling. This will be no different tonight and tomorrow night, as temperatures dip into the 40's.

Cyclonic flow and cold pool aloft will maintain some instability over New England tomorrow, so similar to today, we will likely see a diurnal increase in clouds. However, moisture is very limited, so precipitation is not expected.

Wednesday, cyclonic flow departs / negative vorticity advection. Surface high pressure will move into place. The column will be very dry so should maintain sunny skies through the day. Highs making it to the upper 70's.

By Wednesday night, winds back to the southwest ahead of the next piece of energy dropping into the Great Lakes. This will transport warmth and moisture northward overnight and into Thursday morning. Expect clouds and showers through the morning. The cloudiness should limit high temperatures despite 850mb temps reaching 15C. Surface based instability may lack as a result, however cold air aloft should help elevated convection to develop and a chance for thunderstorms has been inserted into the forecast accordingly.

Friday through Saturday, shortwave remains to our west, but there is more confusion in the model guidance as to a focus for precipitation over the region. We will have the moisture available, but organized precipitation remains questionable. At this point kept Friday dry but cloudy and showers possible Saturday. Sunday, the trough lifts northeast which could drag a final boundary across the region triggering a few showers. In addition, model guidance has been developing a wave along the boundary and riding it northeast, which could mean an even wetter forecast mainly for eastern New England.

Monday, should see partial clearing with dry conditions. Pattern-wise, model guidance continues to push toward more zonal flow by next week. Although maintaining above normal high latitude heights, below normal heights begin building over polar latitudes / finally a neutralization of the Artic Oscillation. At this point I'm expecting a westward shift in the trough axis toward the Ohio Valley, and ridging building slowly over the west Atlantic.

Nice start to the week, lousy end

2009-07-10T20:30:00.000-04:00

No changes for the weekend. Both Saturday and Sunday look good weather-wise. It'll be Saturday night that features showers and thunderstorms. Highs should reach near 80 both days. Main focus will be the chance for a few afternoon pop-up showers/storms as cyclonic flow remains in the region with positive vorticity advection. The limiting factor for this will be a lack of moisture to work with.

Monday will be a similar situation to Sunday with the potential for a few showers in the afternoon. A slightly better chance with a few more clouds too, so I'd pick Sunday over Monday for a fair weather day. Monday will also be a few degrees cooler.

Tuesday and Wednesday, a second shortwave moves through with the dynamics for showers, but still a lack of moisture. Some diurnal clouds, but should stay dry.

Thursday through Sunday, we have a shortwave moving through the Great Lakes with surface low pressure developing south of New England. This has the makings for another round of cloudy, damp days.

Overall, perpetual northeast trough remains, and the "Year Without a Summer" continues.

El Nino declared by the CPC

2009-07-09T16:57:00.000-04:00

EL NIÑO/SOUTHERN OSCILLATION DIAGNOSTIC DISCUSSION

Synopsis: El Niño conditions will continue to develop and are expected to last through the Northern Hemisphere Winter 2009-2010.

During June 2009, conditions across the equatorial Pacific Ocean transitioned from ENSO-neutral to El Niño conditions. Sea surface temperature (SST) anomalies continued to increase, with the latest weekly departures exceeding +1.0°C along a narrow band in the eastern equatorial Pacific (Fig. 1). All of the weekly SST indices increased steadily during June and now range from +0.6°C to +0.9°C (Fig. 2). Subsurface oceanic heat content anomalies (average temperatures in the upper 300m of the ocean, Fig. 3) also increased as the thermocline continued to deepen (Fig. 4). Consistent with the oceanic evolution, the low-level equatorial trade winds were weaker-than-average across much of the Pacific basin, and convection became increasingly suppressed over Indonesia. This coupling of the ocean and atmosphere indicates the development of El Niño conditions.

'Normal' temperatures Friday

2009-07-09T09:10:00.000-04:00

At this point, mid 70's and sun would feel warm to us now. However, the normal high for this time of year is in fact in the low 80's. Since June 1, we have hit 80 degrees exactly twice and gone no higher. Finally, low 80's is looking likely Friday and possible Saturday as well.

A departing mid level trough is giving way to surface high pressure sliding into the region today, and then offshore tomorrow. This will help dry out the atmosphere. Today, we still have left over moisture hanging around, but we'll see gradual clearing through the day. Highs today will struggle into the low 70's due to a chilly start and overall mostly cloudy skies. Tomorrow, 850mb temperatures will still be on the cooler side, however we'll see mostly sunny skies helping to heat the surface up into the low 80's. On Saturday, the majority of the day could be dry with mostly sunny skies in the morning, and increasing clouds in the afternoon as a frontal boundary approaches from the west. The timing of the front will bring the main round of showers and thunderstorms overnight Saturday. The timing of clouds will determine the high for the day, so if there is enough of a cap through the afternoon, we could hit the low 80's again. We'll have to watch for severe potential Saturday night, however nocturnal events require stronger daytime instability and a strong cold pool aloft (which will not be present this time). Strong vertical shear may help maintain a line through the region nonetheless.

Sunday, some low level moisture will remain, so morning fog possible, followed by afternoon sun. Cold air advection behind the front will prevent us from reaching 80, but upper 70's is likely. Same will go for Monday, although a weak disturbance may trigger a few showers late Monday evening. Moisture will be lacking, so kept the forecast dry for now.

Tuesday through Wednesday, model guidance becomes less agreeable yielding uncertainty in the forecast. The ECM keeps the forecast dry through this period, while the GFS is advertising a small disturbance running a convective complex through the region. Made few changes to the forecast for now, and will wait for better agreement.

Expecting generally a more zonal flow for the nation next week which is welcomed news for the northeast. This will help run storm systems through quicker and not leave an upper low hanging over the region for days and days. Still, overall pattern of ridge - trough across the CONUS will remain with below normal temperatures likely to continue in the east.

The 'upper low' beat goes on

2009-07-07T19:59:00.000-04:00

General pattern of below normal heights over the northeast and southern Canada is expected to continue for the next ten days. This will keep stormy weather and below normal temperatures in the region.

Wednesday... A continued onshore flow provided by inverted surface trough will keep clouds over eastern New England. Shortwave drops into the region with the core of cold air aloft overhead. This will provide enough instability for another round of showers and thunderstorms toward the afternoon. Vertical shear will be less robust than today, nevertheless cannot rule out a few strong to severe cells. Abundant moisture will allow for very heavy downpours to accompany thunderstorms.

Thursday... High pressure noses south into New England. We'll deal with low level moisture early. Otherwise should clear out in the afternoon. Early clouds and 850mb temperatures under 10C will hold highs to the low 70's.

Friday... A warm up. Surface high pressure will be in control over New England with mid level ridging sliding east through the day. Partly to mostly sunny skies should help highs into the upper 70's.

Saturday... Next system moves in from the west, dragging a cold front through the region in the afternoon. Warmer temperatures should surge northward out ahead of the front, so despite increasing clouds, we could touch 80 before storms move in. We'll have to monitor severe potential.

Sunday... front will clear the area in the morning. Upper level low will be further north than the previous series, so we will not have the same instability and moisture is also indicated to be on the low side. Overall, could end up being a nice day, but moisture levels remain to be seen.

Monday and Tuesday, the upper low drops further south into southern Quebec, and cold air aloft centers back over the region. Still, looking at relatively low available moisture. Could be an afternoon shower provided any increase in moisture. 850mb temperatures will be well below normal, so we'll need sunshine to push into the mid 70's.

Upper low lifts northward on Wednesday, giving way to more zonal flow across the nation. Weak disturbances will move quickly through. Heights will still be supressed southward, so continued below normal temperatures.

A matter of destabilization

2009-07-06T19:00:00.000-04:00

I have limited time at the moment, but should have more this evening, and for certain tomorrow.

An upper level low will be dropping southeast toward the region tomorrow with its associated cold pool aloft. 500mb temperatures are projected between -15C and -17C. Meanwhile, low level southerly flow will transport moisture into southern New England, raising dew points into the low 60's. Surface temperatures are more uncertain as factoring in cloud cover will greatly limit highs for the day. Any sunshine however, and we could see decent instability develop. The mesoscale ETA has backed off instability, with a narrow CAPE profile for Keene. However, should we get sunshine, CAPE could reach 1000J/kg easily considering cold air aloft. Plus, the moist low levels will contribute to a very low LCL (between 100 and 300m). Again, it's all a matter of getting sunshine.

The wind profile tomorrow continues to look impressive. Starting at the surface, we have a moderate low level jet poking into the region from the south / southeast. The first kilometer is under 15kt southerly flow, turning to the southwest around 20kt between 1 and 2km. Above 2km, the winds become more unidirectional but increase to around 30 to 35kt through the mid levels. This is all under the left front quadrant of a 100kt westsouthwest upper level jet. Indeed, given destabilization tomorrow, it could become very very interesting. This includes the threat for large hail and damaging winds, as well as a few isolated tornadoes.

Watching t'storm chances

2009-07-06T11:47:00.000-04:00

I have limited time for a discussion right now. At the moment, I'm working on the severe weather outlook for tomorrow, which could be interesting just to give a heads up.

Only small changes to the forecast. Added a chance for thunderstorms on Wednesday as the cold pool aloft stays with us and diurnal instability allows for afternoon convection. Thursday through Saturday look more summery. Timing of the next front by the weekend is still uncertain. Saturday could end up dry, but kept thunderstorms in the forecast.

Sunny skies finally

2009-07-05T09:21:00.000-04:00

You might say that the weather is more autumn-like at this point. With the frontal passage yesterday, winds have picked up out of the west / northwest and have transported drier and cooler air into the region. Skies this Sunday morning are a perfect blue, indicative of dry air. The only difference between now and autumn is that solar heating is much stronger, so regardless of cold air advection, highs will still rebound into the upper 70's.

Monday will be similar to today through at least the afternoon. By evening, clouds will be on the increase with a chance of showers and thunderstorms associated with the next incoming shortwave. Cold pool aloft with decent surface instability will allow showers and thunderstorms to continue on Tuesday. High temperatures will be kept down in the mid 70's due to clouds. Cold air aloft sticks around Wednesday, so an afternoon shower or storm cannot be ruled out. Otherwise, partly cloudy skies, highs in the mid 70's.

On Thursday, high pressure slides to our east, with ridging nosing in from the center of the nation. We should see at least partial clearing, allowing highs to reach the upper 70's. Friday, ridging continues to slide east, however model guidance has become less robust with any "heat". Highs still should reach around seasonal normals, around 80 to low 80's.

There is some disagreement between the timing of the next frontal passage. The GFS has quickened, to pulling it through the region on Friday. The ECM, UKMET and GGEM all hold it off until Saturday. Showers and thunderstorms will be likely with the frontal passage.

By next week, southeast ridging will develop, however the perpetual trough over the northeast will not be restrained, and we will continue to see rounds of unsettled weather and below normal temperatures.

A return to summer weather

2009-07-03T19:35:00.000-04:00

Synopsis:

Partial clearing has returned to the region, and the sun should continue to honor us with its presence through the next week. A chance for showers will be present with the passage of a couple disturbances through Wednesday. Temperatures will be on the rise, reaching above normal by Friday.

Full discussion forthcoming.

Fireworks Forecast

2009-07-03T10:02:00.000-04:00

Finally some sunny skies this morning. However, they will not last long. Mid level cloudiness is advancing from the west out ahead of the next shortwave trough. It will not be the same gray sky dreariness as yesterday at least. With southwesterly winds, temperatures will be rebounding up into the mid 70's. This is still 5 degrees below the normal for today, but it will certainly be welcomed after sitting in the 60's most of yesterday.

As for precipitation chances, the frontal boundary moving slowly eastward will trigger scattered showers and thunderstorms this afternoon. Vertical shear is fairly weak so we will not see much in the way of organized lines, but rather single cells and small multicell clusters. Cold air aloft will allow for small hail to be a threat in any stronger thunderstorms. Available moisture levels will be lower than the past few days, so not expecting the same washout conditions, but storms will also be slow moving, so any that do develop could be a threat for flash flooding.

So what about for the festivities in Keene? At this point, the main period for showers and storms looks like between 2pm and 6pm. After that, the best dynamics will be offshore, and with decreasing instability with the loss of daytime heating, the thunderstorm threat will be limited. I think we could escape Mother Nature's fireworks to have our own.

An updated weekend forecast will be posted shortly.

When will the wet weather end?

2009-07-02T09:37:00.000-04:00

This question has been asked many times by many people in the northeast over the last week (Answer further down). A perpetual upper low near the northeast has locked in the clouds and rain. Training of showers and thunderstorms has resulted in some areas picking up 4 to 8 inches of rain over the last week. Flash flood warnings are out for much of New England this morning as another batch moves through.

A short wave rotating around the upper low is moving off the Mid Atlantic coast this morning and will passing to our southeast this afternoon. Associated surface low pressure is located south of Long Island generating warm air advection underneath the cold pool aloft. This instability along with abundant moisture is producing heavy showers and thunderstorms. As the shortwave moves to our east, showers will become less widespread this afternoon.

The upper low lifts northeast on Friday, allowing warmer temperatures and a chance for showers and thunderstorms as a frontal boundary crosses during the day. Right on cue, the next upper low drops in on Saturday. This one will be a tighter circulation, powering a strong jet south of the region. Along with cold air aloft, and still plenty of atmospheric moisture, showers and thunderstorms will be possible during the day.

Sunday ... a break. The ECM has shifted toward the GFS in drying out the column on Sunday as the upper low departs. Partly to mostly sunny skies can be expected with highs in the mid 70's. The next disturbance will be rotating northeast from the Mid Atlantic region with showers Monday night into Tuesday.

After that, we could finally see a taste of summer warmth. Ridging will slide east toward the end of next week, with zonal flow across the CONUS and increasing temperatures for New England.

The rain continues

2009-07-01T09:21:00.000-04:00

Synopsis:

An upper level low continues to hang tight over the Great Lakes while low level disurbances rotate around it toward New England. Today and Thursday will feature clouds and frequent showers with temperatures around 10 degrees below normal. A slow warmup through the weekend and next week will follow as the upper low lifts northeast.

Discussion:

Shortwave approaching from the lower Ohio Valley today will provide isentropic lift over the region today. With abundant low level moisture and PWATs climbing to 1.5" this afternoon, we'll see frequent showers today, heavy at times. Today will feature clouds through the day, keeping temperatures in the upper 60's to near 70 which will strongly limit surface based instability. However, with the cold pool of air aloft, elevated convection will be possible this afternoon, and some of these storms could produce hail and gusty winds. Certainly they will produce downpours, and we will likely see some flash flood warnings issued in the northeast once again today.

On Thursday, very similar conditions to today. The upper level low will be in the process of weakening and openning up, while advancing eastward. This will allow a front to cross the region, again increasing isentropic lift and triggering a round of showers and thunderstorms, downpours possible, as always. Persistent clouds as a warm frontal boundary remains to our south will keep highs again down around 70.

The upper low will continue openning and lifting to the northeast on Friday, however it will also continue to affect our region with cold air aloft, cyclonic flow, and abundant moisture keeping clouds and showers/thunderstorms in the forecast. However, temperatures will rebound back into the mid to upper 70's ahead of ... the next upper low.

On Saturday the next chapter of upper lows begins. The low will bring a reinforcing shot of cold air aloft, with a strong jet providing upper level divergence over the region. This will generate showers and afternoon thunderstorms. Winds out of the west will still try to bring a few periods of sun, and will help temperatures into the mid 70's.

Disagreement between the GFS and ECM comes into play by Sunday with the GFS keeping flow more zonal while the ECM is more robust with the amplitude of the upper low. Per the GFS, Sunday would be dry, with partial clearing. Per the ECM, clouds and showers remain. Monday, a second piece of energy rotates south into the region bringing clouds and showers. Tuesday, we could dry off, but temperatures will remain on the cool side behind the low. Wednesday, the ridging over the central US begins pushing eastward with surface high pressure moving into the Ohio Valley. This should be the start of a warm up back to seasonal or slightly above normal temperatures by the end of next week.

6/30 Tropical Atlantic Outlook

2009-06-30T17:28:00.000-04:00

The Atlantic basin is back to a very quiet period. A frontal boundary sagging southward continues to produce convection from the northeast Gulf to Bermuda. An upper level low near 25N/45W is controlling the weather across much of the central basin. To its south, an abundance of dry air is keeping things quiet from 30W to 50W north of 10N while the ITCZ is generating scattered moderate convection south of 10N. A tropical wave that exitted the west African coast on Sunday is positioned near 30W. Convection is confined to the ITCZ while a bare circulation is visible near 10N/33W. Another wave is located near 10N/55W. Moisture is outrunning the wave axis and the disturbance is rapidly losing organization. A third tropical wave is located along 75W in the east-central Caribbean. It is very much devoid of convection while a bare circulation is visible near 16N/76W.

No tropical cyclone development is expected through Friday.

Storms firing, CT bullseye?

2009-06-30T13:05:00.000-04:00

Multiple clusters of severe thunderstorms have sprung up from eastern PA into central NY. The SPC has placed these areas along with far western New England in a severe thunderstorm watch.

At the moment, stratus clouds remain locked in over eastern MA and most of NH and ME. These areas are struggling to reach even the 70's. Meanwhile, the sun has been out across CT and western MA where temperatures have reached the mid to upper 70's and are on their way to highs in the low 80's. The Keene area remains on the boundary between these two air masses. The sun has peaked out once or twice, with temperatures in the low 70's at the moment. We should see some more sun this afternoon before convective influences rebuild the clouds back over us. There remains a decent influx of low level moisture with dew points in the low to mid 60's across most of southern New England up into western NH and VT. This is aided by a 20kt southeasterly low level jet from Long Island into western New England. This flow, with a southwesterly 500mb jet is producing 30 to 40kt of shear.

With moderate dew points and rising surface temperatures, surface CAPE has already eclipsed 1000J/kg over western New England and up to 2000J/kg now over CT and southwest MA. An 3km EHI of 3 has shown up in northern CT as of noon EDT which is suggestive of a high severe weather potential. Anybody with interests in southwestern New England today should closely monitor the development severe weather situation this afternoon.

Tracking severe weather

2009-06-30T09:05:00.000-04:00

With a cold pool of air aloft and the next shortwave trough rotating toward the region, severe thunderstorms will be possible today across eastern New York into western New England. The main deciding factor for thunderstorm intensity will be the extent destabilization through this afternoon. Stratus clouds have a lock on much of New England this morning, and if they take a long time breaking up, surface high temperatures could be more restricted. Otherwise, thunderstorms will move into the area primarily after 2pm, with the main threat being large hail (See the SEVERE WEATHER OULOOK for more details)

This will be a brief discussion for the updated forecast. There are very few changes that have been made for the next 6 days, however beyond that the forecast becomes more uncertain. The ECM in the last 24 hours has cooled the forecast down signficantly with the upper low sliding further south in the long term, and 850mb temperatures being driven back to around 6C. Even with sunny skies, this would only support highs around 70. I am hesistant to go that extreme, but certainly cooled the forecast highs a few degrees. As expressed in the previous discussion, model guidance is definitely unsteady for the day 6-10 period.

Severe t'storms, hail tomorrow

2009-06-29T17:17:00.000-04:00

A strong upper level low sitting over the Great Lakes is providing a cold pool aloft with 500mb temperatures around -15C. The low is generating a 40kt mid level southwesterly jet across the northeast while a 995mb surface low produces southerly / south-southeasterly flow into southern New England. Abundant low level moisture combined with periods of sunshine tomorrow will destabilize the atmosphere with afternoon surface CAPE of 1000J/kg to 1500J/kg. This is a classic set up for a round of strong to severe thunderstorms to the southeast of the upper low, intersecting the low level jet. In this case, the severe threat area extends across most of New York State into western and southern New England.

With the deep cold pool aloft, the primary threat with any thunderstorms will be large hail. Damaging wind gusts are also possible and depending on the extent of the easterly component on the low level winds, we could see a tornado or two develop.

6/29 Tropical Atlantic Outlook

2009-06-29T13:15:00.000-04:00

Invest 93L has become more disorganized over the last 24 hours, and its no longer recognized as a threat for tropical cyclone development. The moisture remanants of the wave will be pulled into the east coast trough, contributing to rainy weather across the southeast.

Elsewhere in the Atlantic, dry air and shear has a strangle hold on much of the central basin. Subsidence in assocation with confluent flow aloft is keeping the Caribbean devoid of any convection.

A new interest has moved off the African coast yesterday and although convection has waned, a low level turning remains well defined with an inverted v signiture in the low clouds.

Improving toward the weekend

2009-06-28T18:56:00.000-04:00

Synopsis:

Continued easterly flow is keeping clouds locked in over central and eastern MA, NH, and ME this afternoon, with peaks of sun further west and south. This general pattern will continue through the week with improving weather and warmer temperatures toward the weekend.

Discussion:

Upper level low sitting over New England will be sliding east tomorrow. However, surface low to our east will hold tight, keeping flow coming in off the ocean. This will lock in clouds over the eastern half of the region while some peaks of sun will be possible over western New England into New York. The next upper low will drop into the Great Lakes region with surface occluded surface low over southern Ontario. With the frontal boundary to our west and any diurnal instability that develops, we will see another round of showers and thunderstorms in the afternoon. Highs will be similar to today, generally in the mid 70's. Shower activity should break up overnight with the loss of daytime heating. Lows dropping into the upper 50's.

The remains of the last low will decay and slide east while the upper low over the Great Lakes sags southward. We actually could get a stretch of partial clearing as winds turn to the west and the next boundary approaches. With the help of some solar radiation, we could see decent instability develop toward the afternoon, and a round of thunderstorms, possibly strong. Highs will rebound into the upper 70's.

On Wednesday, not much change in the position of the upper low over the Great Lakes. Triple point low pressure will develop by Monday Night and slide northeast under New England on Wednesday. This will renew easterly flow over the region with clouds and cooler temperatures than Tuesday. Again, there will be a chance of showers and possibly a thunderstorm.

Thursday through Saturday will feature improvement as the upper low weakens and lifts northward. We will still have to contend with clouds and scattered showers, but temperatures will be on the rebound and by Saturday we'll be up into the upper 70's with partial sunshine.

By Sunday, the low will be mostly out of the way, and we could get through the day dry and with partly to mostly sunny skies. At this point, model guidance becomes shakier, with some suggesting a break down of the block to our east while others hold it up and keep below normal heights over New England. At this point I tend to think a return to seasonally normal temperatures is likely next week, but any real warm up will hold off until later in the month.

6/28 Tropical Atlantic Outlook

2009-06-28T09:39:00.000-04:00

Invest 93L was centered at 20.7N/88.0W at 12z, over the northeast Yucatan Peninsula. Convection has waned over the last 24 hours, and the disturbance is very disorganized at the moment. Development of 93L is unlikely for the next 24 hours while it interacts with land. Once it moves into the Gulf of Mexico, it still has a decent opportunity for development however model guidance has backed off any notable intensification. Invest 93L is currently moving northwest, south of a mid level ridge. Models break down the ridging by hour 36. This will weaken the steering currents over 93L while it is in the central Gulf of Mexico. There is still disagreement on where it goes from there. Especially with the trend towards a more shallow disturbance, some models continue to take it slowly northwest toward Texas / Louisana, while others have it being picked up by the upper low sagging southward over the eastern US, whisking it toward Florida by the end of next week. Regardless, at this time it does not look like 93L will be making a notable impact aside from a period of showers and thunderstorms.

Elsewhere in the Atlantic, a large upper level low continues to produce strong shear over the central basin. The southern and eastern Caribbean remain dry and devoid of convection. Clusters of weak thunderstorms are present along the ITCZ between 55W and 60W and 30W and 35W. A wave exitting the African Coast is generating moderate convection between 15W and 20W.