Final Pattern Change

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/splillo

Brief icy conditions possible tomorrow morning

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

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

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

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

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

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

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

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?

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

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

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

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

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

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

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?

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

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

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

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".