893
FXUS61 KBOX 091521
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
1021 AM EST TUE FEB 9 2010
SYNOPSIS
DRY AND SEASONABLY COOL WEATHER WILL PREVAIL TODAY. A RAPIDLY
INTENSIFYING COASTAL STORM WILL BRING SIGNIFICANT SNOW AND STRONG
WINDS TO PORTIONS OF SOUTHERN NEW ENGLAND...WITH AREAS ALONG AND
SOUTH OF THE MASS TURNPIKE MOST AT RISK FOR SUBSTANTIAL AMOUNTS.
HIGH PRESSURE THEN BRINGS DRY AND SEASONABLY COLD WEATHER THURSDAY
THROUGH THE WEEKEND.
NEAR TERM /UNTIL 6 PM THIS EVENING/
12Z OBSERVED SOUNDINGS FROM CHH AND ALY SUPPORT PREVIOUS FORECAST
HIGHS OF LOW TO MID 30S ACROSS MUCH OF THE REGION WITH ABUNDANT
SUNSHINE. PRES GRADIENT SLOWLY RELAXES THIS AFTERNOON WITH WINDS
BECOMING LIGHT AND VARIABLE BY 4-5 PM. PREVIOUS DISCUSSION BELOW.
SFC AND MID LEVEL RIDGE BUILDS EWD ACROSS SNE THIS AFTERNOON. EXPECT
MOSUNNY SKIES AND SEASONABLE TEMPS WITH SOME HIGH CLOUDS MOVING IN
FROM THE SW LATE TODAY. GUSTY NW FLOW WILL RAPIDLY DIMINISH BY THIS
AFTERNOON. USED MAV/MET BLEND FOR TEMPS.
SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/
TONIGHT...CYCLOGENESIS TAKES SHAPE OFF MID ATLC COAST AS POTENT MID
LEVEL LOW MOVES TOWARD THE COAST WITH TREMENDOUS HEIGHT FALLS
DEVELOPING. CLOUDS THICKEN AND LOWER WITH SNOW APPROACHING SW ZONES
TOWARD 12Z. NAM LOOKS TOO SLOW WITH PRECIP ONSET WHICH IS A TYPICAL
BIAS OF THE NAM SO WE LEANED TOWARD A BLEND OF THE GFS/SREF BRINGING
CHC POPS NWD TO BDL-PVD-EWB TOWARD DAYBREAK AND DRY TO THE NORTH.
HEAVIER SNOW SHOULD HOLD OFF TIL AFT 12Z AND MOST OF THE EARLY
MORNING COMMUTE FROM HFD TO PVD SHOULD BE OK.
LONG TERM /WEDNESDAY THROUGH MONDAY/
MAIN FORECAST CONCERNS REVOLVE AROUND SNOW AND WIND POTENTIAL FROM
POTENT COASTAL STORM WEDNESDAY AND WEDNESDAY NIGHT.
7 AM UPDATE...
WE HAVE REVIEWED SOME ADDITIONAL DATA REGARDING THE UPCOMING STORM.
THERE ARE STILL A LOT OF MIXED SIGNALS WITH RESPECT TO HOW FAR NORTH
THE HEAVIEST SNOW IS GOING TO GET ON WEDNESDAY. MOST OF THE DATA
STILL POINT TOWARD A WARNING EVENT FOR OUR SOUTHERN ZONES...MAINLY
CLOSER TO THE SOUTH COAST. HOWEVER...WE FEEL THAT A SLIGHT NORTHWARD
EXPANSION TO THE WATCH IS WARRANTED BASED ON SOME NEWER DATA. JUST DO
NOT LIKE HOW THE ENSEMBLES ARE MODELING A 4 TO 5 STANDARD DEVIATION
TO THE EASTERLY LOW LEVEL JET ON WEDNESDAY...ALONG WITH PWAT
ANOMALIES OF +1 TO +2 SD. THIS MAY AID IN HEAVIER PRECIPITATION
ADVANCING A BIT MORE NORTH THAN THE CURRENT MODEL CONSENSUS
INDICATES...PERHAPS MORE LIKE THE 00Z AND 06Z GFS ENSEMBLE...WHERE
NEARLY EVERY MEMBER HAS AT LEAST A HALF INCH QPF TO BOSTON.
HOWEVER...THE GFS ENSEMBLE MEMBERS MAY NOT BE RIGHT THOUGH...SINCE
MOST MEMBERS PROGGED THE PVD AREA GETTING 0.25 TO 0.50 LIQ EQUIV /24
HOUR FORECAST/ THE OTHER DAY WHEN DC TO PHL GOT THEIR 2 FT SNOWSTORM.
IN THE END WE DIDN/T SEE A FLAKE HERE OUTSIDE SOME SCT OCEAN EFFECT...SO
NOT SURE ABOUT THE RELIABILITY OF THESE ENSEMBLE MEMBERS.
HOWEVER...WE FEEL THERE ARE SOME SIGNALS HERE TO WARRANT A WATCH. THE
DAY SHIFT WILL BE ABLE TO TAKE A LOOK OVER THE DATA AND DETERMINE
WHILE ZONES NEED A WARNING...ADVISORY...OR NOTHING AT ALL.
PREVIOUS DISCUSSION...
STRONG CLOSED UPPER LEVEL LOW WILL RACE TOWARD THE EAST COAST AND
ENTER THE ATLANTIC AROUND THE DELMARVA ON WEDNESDAY. THE WILL AID IN
INDUCING RAPID CYCLOGENESIS WELL TO THE SOUTH OF LONG ISLAND WHICH
WILL RESULT IN A MODERATE SNOWSTORM FOR MUCH OF SOUTHERN NEW ENGLAND
TO THE SOUTH OF THE MASS PIKE. OVERALL...FORECAST RATIONALE HAS NOT
CHANGED MUCH FROM PREVIOUS DAY SHIFT...SO THEREFORE THE FORECAST
HASN/T CHANGED MUCH. THE POSITIONING OF THE MID LEVEL LOW AND IT/S
ASSOCIATED FORCING MECHANISMS WILL DETERMINE HOW FAR NORTH HEAVY
SNOWFALL GETS. THIS IS STILL IN QUESTION AS THERE REMAIN DIFFERING
MODEL SOLUTIONS. OVERALL...WE LIKED A GFS/SREF/GFS ENSEMBLE BLEND THE
BEST.
CATEGORICAL POPS FOR SNOWFALL SHOULD BE KNOCKING ON OUR SOUTHERN DOOR
AT THE START OF THE FORECAST PERIOD AS MID LEVEL WARM FRONT SHARPENS
UP TO THE SOUTH OF LONG ISLAND. AS THIS FORCING MECHANISM MOVES
NORTHWARD DURING THE MORNING HOURS...HEAVY SNOWFALL...POSSIBLY BANDED
IN A WEST TO EAST FASHION SHOULD ALSO BE MOVING NORTHWARD THROUGH LI
AND SOUTHERN CT WITH 1+ INCH PER HOUR SNOWFALL RATES. NOT COMPLETELY
SURE HOW FAR NORTH THIS BAND WILL MAKE IT IN STOUT FORM...BUT WE
THINK AT LEAST OUR CT/RI/SE MASS ZONES WILL SEE IT DURING THE
AFTERNOON HOURS WEDNESDAY. NORTH OF THERE...IT WILL SNOW...BUT THE
HEAVIER BAND WILL PROBABLY FALL APART AS THE FORCING BECOMES REMOVED
FROM THE MAIN SYSTEM.
AT THIS TIME...IT APPEARS AS THOUGH THE MID LEVEL LOW REALLY CRANKS
UP A SMIDGE TOO FAR SOUTHEAST OF THE REGION TO ALLOW FOR A PROLONGED
PERIOD OF HEAVY SNOW OVER THE MAJORITY OF SOUTHERN NEW ENGLAND.
THEREFORE...WE THINK THE BEST CHANCE OF WARNING CRITERIA SNOWFALL
REMAINS SOUTH OF THE MASS PIKE. THAT/S WHERE THE DAY SHIFT INITIALLY
HOISTED WATCHES...AND WE SEE NO NEED TO EXPAND NORTHWARD AT THIS
TIME. THE HEAVIEST SNOWFALL IS EXPECTED TO FALL FROM LATER WEDNESDAY
MORNING INTO WEDNESDAY EVENING BEFORE TAPERING OFF AND ENDING AFTER
MIDNIGHT WEDNESDAY NIGHT. THE CAPE AND ISLANDS MAY SEE LOWER SNOW
ACCUMS DUE TO A WARMER BOUNDARY LAYER...ALTHOUGH WE THINK THOSE TEMPS
WILL TURN COLDER IF BANDING DEVELOPS LATE WED AND WED EVENING.
FORECAST SNOWFALL TOTAL GRAPHICS ARE POSTED TO THE WEB. THESE WILL
PROBABLY HAVE TO BE ADJUSTED EITHER NORTH OR SOUTH WITH TIME
DEPENDING ON EXACTLY HOW AND WHERE THE SYSTEM EVOLVES. DETAILS ARE STILL
UNCERTAIN...AND WE WOULDN/T BE SURPRISED TO SEE THE HEAVIEST SNOWFALL
AXIS SHIFTED 50 OR SO MILES NORTH OF SOUTH OF WHERE IT/S CURRENTLY
FORECAST TO OCCUR. THEREFORE...FOLKS ALONG AND NORTH OF THE PIKE
SHOULD STILL BE ON THE LOOKOUT FOR POSSIBLE FORECAST CHANGES AND/OR
HAZARDS. CONVERSELY...A 50 MILE SHIFT SOUTH...KIND OF WHAT THE GGEM
AND ECMWF SHOWS...WOULD ALLOW FOR MUCH OF THE WATCH AREA TO BE
LOWERED TO AN ADVISORY AT SOME POINT TODAY OR NIGHT.
THE WEDNESDAY MORNING RUSH HOUR WILL PROBABLY BE OKAY...BUT THE
EVENING RUSH HOUR WILL PROBABLY BE A MESS WITH LOW VSBYS...INCREASING
WINDS...AND SNOW COVERED ROADWAYS...MAINLY SOUTH OF THE PIKE.
THE WIND IMPACTS COULD BE SIGNIFICANT...ESPECIALLY ON THE CAPE AND
ISLANDS WHERE LOCAL GUST TOOLS ARE SHOWING POTENTIAL FOR 50 KNOT
GUSTS LATE WED AFTN AND NIGHT. WE HAVE THEREFORE ISSUED A HIGH WIND
WATCH FOR THAT AREA. NO BLIZZARD WATCH AT THIS TIME BECAUSE WE ARE
NOT SURE WE WILL MEET THE VSBY CRITERIA SINCE BL TEMPS WILL BE WARMER
THERE CAUSING POTENTIAL PRECIP TYPE ISSUES. FURTHER INLAND...ADVISORY
WIND SPEEDS WILL BE POSSIBLE.
AFTER THE STORM DEPARTS LATE WEDNESDAY NIGHT WE LOOK TO BE IN FOR A
RELATIVELY QUIET PERIOD OF WEATHER WITH NEAR TO BELOW NORMAL
TEMPERATURES AND FAIR WEATHER.
AVIATION /15Z TUESDAY THROUGH SATURDAY/
TODAY...HIGH CONFIDENCE VFR. GUSTS TO 20-25KT THRU 20-21Z THEN WIND
BECOMING CALM OR LIGHT/VARIABLE.
TONIGHT...HIGH CONFIDENCE VFR MOST OF THE NIGHT WITH GRADUAL
LOWERING CIGS. MVFR APPROACHING N CT TO SW RI TOWARD 12Z IN
DEVELOPING SNOW.
OUTLOOK...WEDNESDAY THROUGH SATURDAY...
WEDNESDAY AND WEDNESDAY NIGHT...MODERATE TO HIGH CONFIDENCE IN IFR
CONDITIONS IN SNOW ACROSS MOST TERMINALS...BUT CONDITIONS ACROSS MHT
ARE MORE UNCERTAIN. NORTHEAST WIND GUSTS OF 35 TO 45 KNOTS ARE
POSSIBLE ACROSS THE COASTAL TERMINALS...ESPECIALLY ON THE CAPE AND
ISLANDS.
THURSDAY...EXPECT CONDITIONS TO IMPROVE TO VFR ACROSS MOST LOCATIONS
BY EARLY TO MID MORNING...POTENTIALLY BEFORE SUNRISE WITH THE
POSSIBLE EXCEPTION OF HYA/ACK.
FRIDAY AND SATURDAY... HIGH CONFIDENCE OF VFR.
MARINE
TODAY...WIND GUSTS 25-30 KT WILL PERSIST THROUGH 12Z BEFORE
GRADUALLY DIMINISHING WITH WINDS BELOW 20 KTS THIS AFTERNOON AS
GRADIENT RELAXES. SCA EXPIRES 13-18Z. SEAS SUBSIDING TO BELOW 5 FT
THIS AFTERNOON OUTER WATERS.
TONIGHT...LIGHT WINDS BECOMING NE 15-20 KT OVER SW WATERS TOWARD
DAYBREAK AS COASTAL LOW DEVELOPS TO THE SOUTH.
OUTLOOK...WEDNESDAY THROUGH SATURDAY...
WEDNESDAY AND WEDNESDAY NIGHT...LOW PRESSURE BOMBING OUT TO THE
SOUTH OF THE BENCHMARK WILL RESULT IN VERY STRONG WINDS AND HIGH
SEAS. HIGH CONFIDENCE IN NORTHEAST WIND GUSTS OF 45 KNOTS ACROSS
MOST OF OUR OPEN WATERS. THE POTENTIAL FOR OVER 50 KNOT WIND GUSTS
EXISTS WEDNESDAY NIGHT...THEREFORE WE HAVE ISSUED A STORM WATCH.
INCREASED SEAS OVER WNA GUIDANCE WED NIGHT INTO THURS. COULD SEE UP
TO 25 FT EAST OF THE CAPE AND ISLANDS.
THURSDAY...NORTHWEST GALE FORCE WIND GUSTS SHOULD DIMINISH BY LATE
MORNING OR AFTERNOON...BUT SCA WINDS CONTINUE.
FRIDAY AND SATURDAY...SEAS ON THE OUTER WATERS SHOULD SUBSIDE TO
BELOW 5 FT. NORTHWEST WINDS MAY GUST TO NEAR SMALL CRAFT ADVISORY
THRESHOLD LIMITS OF 25 KNOTS THROUGH THE PERIOD.
TIDES/COASTAL FLOODING
TIDES WILL PEAK AT 2-2.5 FT ABOVE NORMAL ACROSS THE EASTERN MA COAST
WED NIGHT INTO THU MORNING WITH 20+ FT SEAS DEVELOPING JUST OFFSHORE
BY LATE WED NIGHT. NO PROBLEMS ARE ANTICIPATED DURING THE WED EVENING
HIGH TIDE AS THIS IS A LOW ASTRO TIDE AND SEAS WILL JUST BE IN THE
PROCESS OF RAMPING UP. THE THU MORNING HIGH TIDE IS HIGHER AND
ALTHOUGH WINDS WILL BE SHIFTING TO THE N/NW...A STORM SURGE OF 2 FEET
AND 15-20 FT SEAS COULD RESULT IN SOME MINOR COASTAL FLOODING AS A
WORST CASE SCENARIO...PARTICULARLY FROM THE OUTER CAPE TO ACK WHERE
THE HIGHEST SEAS WILL BE.
BOX WATCHES/WARNINGS/ADVISORIES
CT...WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH LATE
WEDNESDAY NIGHT FOR CTZ002>004.
MA...WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH LATE
WEDNESDAY NIGHT FOR MAZ012-013-015>024.
HIGH WIND WATCH FROM WEDNESDAY AFTERNOON THROUGH LATE
WEDNESDAY NIGHT FOR MAZ022>024.
NH...NONE.
RI...WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH LATE
WEDNESDAY NIGHT FOR RIZ001>008.
MARINE...STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH LATE WEDNESDAY
NIGHT FOR ANZ231>235-250-254>256.
GALE WATCH FROM WEDNESDAY MORNING THROUGH LATE WEDNESDAY NIGHT
FOR ANZ230-236-237-251.
SMALL CRAFT ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR ANZ250-
254>256.
SYNOPSIS...KJC/EKSTER
NEAR TERM...KJC/NOCERA - UPDATED 1016 AM
SHORT TERM...KJC
LONG TERM...EKSTER
AVIATION...KJC/NOCERA/EKSTER
MARINE...KJC/EKSTER
TIDES/COASTAL FLOODING...
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