http://www.hpc.ncep.noaa.gov/wwd/day2_composite.gif
http://www.hpc.ncep.noaa.gov/wwd/day3_composite.gif
MAP READ OUT FOR KEENE, NH
For Sunday:
Moderate (>40%) chance of >4"
Slight (>10%) chance of >8"
For Monday:
High (>70%) chance of >4"
High (>70%) chance of >8"
Moderate (>40%) chance of >12"
*usually the moderate chance values verify, in which case we would be talking about 20 inches of snow here.
HPC Heavy Snow Discussion...
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
529 PM EDT FRI APR 13 2007
VALID 00Z SAT APR 14 2007 - 00Z TUE APR 17 2007
- snip -
DAY 2...
EAST...
THE MODELS CONTINUE TO ADVERTISE THE AMPLIFICATION OF THE DEEP
LAYER TROUGH CROSSING THE OH VALLEY WITH A 90-110 KT JET MOVING UP
THE EAST COAST AS A NEW LOW LEVEL CYCLONE DEVELOPS OVER THE MID
ATLANTIC STATES AND RAPIDLY INTENSIFIES. THIS WILL LEAD TO THE
RAPID DEVELOPMENT OF AN AREAS OF MODERATE TO HEAVY PRECIPITATION
OVER THE NORTHERN MID ATLANTIC STATES AND SPREAD INTO NY-SRN NEW
ENGLAND. THERE ARE STILL TRACK/TIMING DIFFERENCES TO BE RESOLVED
WITH THE GFS A FEW HOURS FASTER/CANADIAN GLOBAL A FEW HOURS SLOWER
WITH THE LOW MOVING UP THE COAST...IMPACTING BOTH PRECIP AMOUNTS
AND THERMAL PROFILES. MANUAL PROGS USED A BLEND OF THE 00Z-12Z
ECMWF/12Z-18Z NAM/GFS PARALLEL
PRECIP AMOUNTS/THERMAL PROFILES...WHICH FAVOR HEAVY SNOW
DEVELOPING IN INTERIOR SOUTHEAST NY AND NORTH CENTRAL PA.
UNCERTAINTIES ALSO OCCUR WITH RESPECT TO ELEVATION...AS SEVERAL
AREAS IN THE HIGHER TERRAIN OF NORTHWEST CT/CENTRAL TO WEST MA
SHOULD LAST AS SNOW LONGER THAN ADJACENT LOWER ELEVATION
LOCATIONS.
DAY 3...
...NORTHEAST...
THE MODELS CONTINUE TO INDICATE RAPID DECELERATION OF THE CYCLONE
MOVING TO NEAR LONG ISLAND/SOUTHERN NEW ENGLAND...WITH A 60-80 KT
EAST JET MOVING ONSHORE COASTAL NEW ENGLAND AND STRONGLY DIFLUENT
FLOW ALOFT...FAVORING HEAVY SNOW ACROSS INTERIOR NEW ENGLAND AND
NORTHERN NEW YORK. THE STRENGTH AND PERSISTENCE OF THE STRONG LOW
LEVEL JET SUPPORT HEAVY TO POTENTIALLY PRODIGIOUS SNOWFALLS IN THE
TERRAIN WHERE THE FLOW TURNS UPSLOPE IN THE WHITE MOUNTAIN AND
GREEN MOUNTAINS/ADIRONDACKS.
WIDE VARIATIONS IN TOTAL IN SNOWFALL ARE EXPECTED DUE TO THERMAL
PROFILE DIFFERENCES
WITH DIFFERENCES IN SNOWFALL DURATION DUE TO WARM LAYERS SFC AND
ALOFT IN EASTERN NEW ENGLAND...COMBINED WITH VARIATIONS RESULTING
FROM UPSLOPE AND DOWNSLOPE FLOW.
MANUAL PROGS CONTINUED TO WEIGHT TOWARDS THE QPF AND THERMAL
PROFILES OF THE 00-12Z ECMWF/12Z GFS PARALLEL/12-18Z NAM
/UKMET/GLOBAL ENSEMBLE MEAN. THE HIGHER RISKS ARE INDICATED IN THE
AFOREMENTIONED TERRAIN WHERE PRECIPITATION MAXIMA HAVE THE HIGHEST
LIKELIHOOD PLUS THERE IS BETTER AGREEMENT AMONG THE MODELS WHERE
IT REMAINS COLD ENOUGH FOR PERSISTENT SNOW. I HAVE INDICATED A
HIGH RISK FOR EIGHT AND TWELVE INCHES IN THE TERRAIN DUE TO THE
SLOW MOTION OF THE CYCLONE AND THE UNUSUALLY HIGH 850 MB MOISTURE
FLUX ANOMALIES OF 4 STANDARD DEVIATIONS ABV NORMAL MOVING ONSHORE
COASTAL EASTERN NEW ENGLAND MONDAY.
- snip -
Meanwhile the NWS in Taunton is in fact downplaying the snow potential, and even downplay QPF a little.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
425 PM EDT FRI APR 13 2007
...MAJOR NOR'EASTER SUNDAY AFTERNOON AND NIGHT WITH UNCERTAINTY ON
WIND/WEATHER/WAVE EVOLUTION MONDAY DUE TO OCCLUSION AND REFORMATION
MODEL GUIDANCE SPREAD...
.SHORT TERM /TONIGHT THROUGH SUNDAY/...
TONIGHT THROUGH SATURDAY NIGHT...CONTINUITY WITH PREVIOUS MORNING
KBOX FCST. USED A BLEND OF NAM AND GFS MOS TEMPS WHICH MODIFIES
SATURDAY AFTERNOONS TEMPS A BIT WARMER. CLEARING TONIGHT THEN CLOUDS
REFORM MIDDAY SATURDAY BUT WITH A BIT WARMER TEMPS PRIOR TO CLOUDS
REFORMING. GUST ALG TOOL WAS RUN OFF THE NAM MXG HTS AND NAM PROFILE
WHICH MAY HAVE OUR WINDS A BIT TOO STRONG TONIGHT AND SAT MORNING
BUT SUFFICE FOR NOW.
SUNDAY...TIMING ISSUES FOR QPF ONSET. USED A 50-50 BLEND OF NAM/GFS.
EC SEEMS TO BE WARMING AND THE UK AND GGEM SEEM TOO FAR SOUTH BUT
THIS IS OPEN TO DEBATE. THEREFORE INCONCLUSIVE ON HOW MUCH WINTRY
PCPN. USED THE NAM MXG HTS FOR WIND AND NAM WIND PROFILE.
HPC IS MORE BULLISH THAN WE ARE REGARDING SNOWFALL POTENTIAL FOR
SNE. AM HESITANT WITH NAM PROFILES BEYOND 18 HOURS...ESP BEING
BURNED YDY BY OVER RELIANCE ON NAM/UKMET/GGEM WHICH WERE ALL COLDER.
WE KNOW THE GFS ENS ARE WARMER /LIKE FOR YDY'S STORM ON WEDNESDAY/.
IN OTHER WORDS...WILL A SIMILAR SCENARIO PLAY OUT...MODELS TREND
NORTH. WE'VE HEARD SOME COMMENT COMPARING TO DEC 1992. WE ARE NOT.
EVOLUTION SEEMS TOO FAR N AT 500 MB AND NOT MUCH SIGN OF NEG
TILTING! ALSO...THAT SYSTEM HAD STRONGER HIGH IN SE CANADA. THE WIND
GENERATED FM THIS SYSTEM IS DUE TO THE INTENSE LOW PRES GRADIENT
DEVELOPED BY A 975-980MB SFC LOW.
ALL MODELS BRING MEASURABLE INTO SNE DURING THE DAY SUNDAY. BL WARMTH
WILL AGAIN BE A PLAYER IN ANY SLEET/SNOW ACCUM. WE ARE CONSERVATIVE.
NO HEADLINES ATTM DUE TO OUR PERCEPTION THAT THE MAIN EVENT IS SUNDAY
NIGHT. THAT WOULD BE 5TH PERIOD. WE ALREADY HAVE CONSIDERABLE PUBLIC
AWARENESS ON THIS STORM.
MID SHIFT CAN GO AHEAD AND WORK ANY WATCHES FM SUN AFTERNOON ONWARD
IF THEY WISH. AGAIN I BURNED ON A 4TH PRD WATCH YDY WHICH ONLY
VERIFIED AS AS A WXA WITH SPOT 5" AMTS FM FRANKLIN COUNTY INTO
CHESHIRE COUNTY.
QPF IS FROM HPC WITH A TRIMMING OF AMTS PRIOR TO 12Z SUNDAY.
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
A MAJOR COASTAL STORM IS EXPECTED TO CONTINUE SUNDAY NIGHT INTO
MONDAY. THERE IS STILL SOME UNCERTAINTY CONCERNING THE TRACK OF
THIS STORM...AND THAT TRACK WILL BE CRITICAL. MOST OF THE LATEST
GUIDANCE CONTINUES TO KEEP THIS LOW PRESSURE JUST SOUTH OF LONG
ISLAND MONDAY MORNING. THE 13/12Z GFS HAS THE FARTHEST NORTH
SOLUTION...WITH THE 13/12Z NAM CLOSE TO THE GFS ENSEMBLE MEAN. THE
12Z GGEM IS THE FARTHEST SOUTH...KEEPING THE STORM ABOUT FARTHER
SOUTH OF LONG ISLAND. 12Z UKMET AND ECMWF ARE IN DECENT AGREEMENT
WITH THE GGEM.
CURRENT THINKING IS THE 12Z GFS IS TOO FAR NORTH WITH ITS
SOLUTION...BUT THE OTHER CAMP OF THE GGEM/UKMET AND ECMWF MIGHT BE A
SHADE TOO FAR SOUTH. HAVE BASED THIS FORECAST ON A TRACK CLOSER TO
THE GGEM...BUT SHIFTED NORTH A SMIDGE TO MAINTAIN SOME CONTINUITY
WITH PREVIOUS FORECAST.
THIS LOW PRESSURE IS EXPECTED TO MEANDER EVER SO SLOWLY SOUTHEAST
MONDAY NIGHT...AFTER BEING PRACTICALLY PARKED AROUND LONG ISLAND
SUNDAY NIGHT AND MONDAY.
TEMPERATURES WILL BE CRITICAL FOR THIS FORECAST...WITH A LOT OF
MOISTURE TO COME DOWN. PRESENTLY THINKING THIS WILL BE MAINLY IN
THE FORM OF RAIN WITH TEMPERATURES ABOVE FREEZING...AT LEAST DURING
THE DAYLIGHT HOURS...FOR THE LOWEST 2-3 KFT. AT THIS TIME THINKING
MOSTLY RAIN...BUT THE TRACK MAY CHANGE THAT IN FUTURE FORECASTS.
STAYED VERY CLOSE TO HPC GUIDANCE TUESDAY INTO NEXT FRIDAY TO FOCUS
ATTENTION ON COASTAL STORM SUNDAY NIGHT INTO MONDAY. A RELATIVELY
MORE TRANQUIL PERIOD...BUT COLDER THAN NORMAL WITH A PERSISTENT
NORTH FLOW.
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