FXUS61 KBOX 091134
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
634 AM EST WED DEC 9 2009
.SYNOPSIS...
A STRONG STORM WILL AFFECT SOUTHERN NEW ENGLAND TODAY WITH A MIX OF
WINTRY PRECIPITATION AND A PERIOD OF STRONG WINDS AT THE COAST.
BLUSTERY AND CHILLY WEATHER WILL FOLLOW THURSDAY INTO EARLY NEXT
WEEK. A PERIOD OF RAIN AND OR SNOW SHOWERS MAY OCCUR TUESDAY IN
ASSOCIATION WITH LOW PRESSURE.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
*** A PERIOD OF HEAVY SNOW FOR MUCH OF SOUTHERN NEW ENGLAND THIS
MORNING FOLLOWED BY STRONG TO DAMAGING WINDS AT THE COAST ***
POWERFUL STORM TO IMPACT THE REGION TODAY WITH SNOW ALREADY
OVERSPREADING MUCH OF CT AND WESTERN MA AT 330 AM. VERY DYNAMICAL
SYSTEM WITH STRONG JET DYNAMICS MOVING ACROSS THE REGION THIS
MORNING. PRIMARY LOW APPROACHING CHICAGO BUT SECONDARY LOW FORMING
ALONG VA COAST AT 330AM IN RESPONSE TO JET DYNAMICS. IN FACT RAPID
DEEPENING TAKING PLACE WITH PRES FALLS OF 9 MB LAST 3 HRS NEAR DCA.
AS FOR MODEL OF CHOICE...AT 06Z NAM THERMAL PROFILES VERIFYING BEST
WITH GFS PRECIP SHIELD MATCHING RADAR AND OBSERVATIONS VERY WELL.
AIRMASS OVER THE REGION IS ONLY MARGINALLY COLD ENOUGH TO SUPPORT
SNOW...HOWEVER STRONG PRES FALLS ASSOCIATED WITH SECONDARY LOW WILL
BACK LOW LEVEL WIND SUFFICIENTLY TO MAINTAIN COLD AIR OVER THE REGION
ESP AWAY FROM THE COAST. THESE PRES FALLS ARE ALSO AIDING THE DEVELOP
OF COLD AIR DAMMING AND POSSIBLE COASTAL FRONT DEVELOPMENT...WHICH
WILL MAKE PTYPE FORECAST VERY DIFFICULT FOR EASTERN COASTAL MA
INCLUDING THE CITY OF BOSTON.
NAM BUFKIT SOUNDINGS SUGGEST PRECIP REMAINING ALL SNOW ACROSS MUCH OF
THE AREA /JUST NORTHWEST OF BOSTON-PROVIDENCE CORRIDOR/ TIL AT LEAST
15Z/10AM. BOTH NAM AND GFS DELIVER COPIOUS AMOUNTS OF QPF THROUGH
THIS PERIOD YIELDING SNOWFALL POTENTIAL OF 4-8 INCHES ACROSS THIS
REGION WITH A LOW PROB OF 10 INCHES. THE 03Z SREF HAVE ALSO SHIFTED
FARTHER SOUTH THEIR PROBS OF 8 INCHES...WITH LOW PROB BLEEDING INTO
NORTHERN CT/NORTHWEST RI AND INTO THE I495 CORRIDOR. GFS IS WARMER
ALTHOUGH COLDER THAN PREVIOUS RUNS.
SEVERAL FACTORS FAVOR THIS COLDER SOLUTION...FIRST PRECIP IS MOVING
IN RAPIDLY AND LARGE QPF WILL LIKELY OCCUR BEFORE A CHANGEOVER. ALSO
WARMING ALOFT AND IN THE BOUNDARY LAYER WILL LIKELY BE OFFSET BY
STRONG DYNAMICAL COOLING ASSOCIATED HEAVY PRECIP. SNOW GROWTH IS NOT
IDEAL...HOWEVER MAGNITUDE OF QPF WILL LIKELY SUPERCEDE THIS ISSUE AS
SNOW GROWTH IS USUALLY MORE CRITICAL DURING MARGINAL QPF EVENTS.
GIVEN REASONING ABOVE DECIDED TO UPSHIFT TO A WARNING FOR 4-8 INCHES
OF SNOW ACROSS NORTHERN CT /INCLUDING GREATER HARTFORD/...NORTHWEST
RI AND INTO THE I495 CORRIDOR OF EASTERN MA...INCLUDING THE REMAINDER
OF CENTRAL MA INTO SOUTHWEST NH. FOR THE CITY OF BOSTON...IT/S
COMPLEX AS ONSHORE COMPONENT WITH SST IN THE MU40S WOULD WARM
BOUNDARY LAYER SUFFICIENTLY FOR SNOW TO RAIN. HOWEVER...STRONG PRES
FALL CENTER TRACKING UP THE EASTERN SEABOARD MAY BE INDUCE A COASTAL
FRONT YIELDING A NORTH WIND. THIS WOULD RESULT IN MORE SNOW FOR
BOSTON. FOR NOW WILL FORECAST 2-4 INCHES AND HAVE NEXT SHIFT MONITOR
LATEST TRENDS. DITTO FOR CITY OF PROVIDENCE AND POINTS EASTWARD INTO
PLYMOUTH COUNTY. FOR CAPE COD AND THE ISLANDS ANY SNOW SHOULD CHANGE
TO RAIN FAIRLY QUICKLY WITH PERHAPS AN INCH OR TWO ACCUMULATION.
REGARDLESS OF SNOW TOTALS...A THREE TO SIX HOUR PERIOD OF HEAVY SNOW
WILL COINCIDE WITH THE MORNING RUSH HOUR RESULTING IN TREACHEROUS
TRAVEL. SNOW WILL CHANGE TO RAIN DURING THE LATE MORNING AND EARLY
AFTERNOON FROM SOUTH TO NORTH. RAIN COULD BE HEAVY AT TIMES ACROSS
CT/RI AND SOUTHEAST MA RESULTING IN POOR DRAINAGE FLOODING.
AS FOR WIND POTENTIAL...WILL UPGRADE HIGH WIND WATCH TO A WARNING AS
ALL MODEL GUIDANCE SUGGEST A PERIOD OF EAST WINDS 30 TO 40 MPH WITH
GUSTS TO 60 MPH ACROSS CAPE COD AND THE ISLANDS FROM LATE MORNING
INTO MID AFTERNOON. WIND ADVISORY REMAIN POSTED FOR THE COASTAL
PLAIN.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/...
TONIGHT...LEFTOVER SNOW AND RAIN SHOWERS WITH CYCLONIC FLOW
PREVAILING BEHIND A DEPARTING CANADIAN MARITIMES LOW. TURNING WINDY
AND COOL. A WIND ADVISORY MAY STILL BE NECESSARY PARTICULARLY THE
CAPE AND ISLANDS WHERE SW WINDS COULD GUST TO 45 KT.
THURSDAY AND THURSDAY NIGHT...A TROUGH WILL CROSS THE AREA DURING THE
LATE AFTERNOON OR EVENING. THIS WILL BRING MUCH COLDER AIR TO THE
REGION. MOISTURE IS FAIRLY LIMITED...BUT COULD SEE SCATTERED SNOW
SHOWERS OR FLURRIES PARTICULARLY THE INTERIOR HIGH TERRAIN WHERE SOME
LAKE MOISTURE WILL BE AVAILABLE. LOW LEVEL LAPSE RATES WILL BE
STEEPENING ALONG THE SOUTH COAST. OCEAN EFFECT SNOW SHOWERS WILL BE
POSSIBLE NEAR NANTUCKET AND MARTHAS VINEYARD AS WEST FLOW PREVAILS.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
THE MID TO LONG RANGE MODELS AND THE ENSEMBLES ARE FAIRLY GOOD
AGREEMENT REGARDING THE MEAN SYNOPTIC SCALE FLOW THROUGH EARLY
SATURDAY...THEN BEGIN TO DIVERGE DAYS 5 THROUGH 7. THE
TELECONNECTIONS CONTINUE TO FAVOR A NEGATIVE NAO PATTERN WITH THE
PNA BECOMING POSITIVE. THIS GENERALLY FAVORS COLDER THAN NORMAL
TEMPERATURES ACROSS THE AREA DURING THE EXTENDED TIMEFRAME.
FRIDAY...BLUSTERY CONDITIONS...A COLD WESTERLY FLOW PREVAILS WITH AS
1000-500MB THICKNESSES DROP DOWN INTO THE 510S! DIURNAL CLOUDS AND
SCATTERED SNOW SHOWERS AND FLURRIES WILL BE POSSIBLE DUE TO CYCLONIC
FLOW AT H85 AND ALOFT WHICH WILL TRANSPORT SOME LAKE MOISTURE INTO
THE REGION. WIND CHILL VALUES WILL BE IN THE TEENS.
SATURDAY...HIGH PRESSURE BUILDS ACROSS THE AREA...A DRY DAY EXPECTED
BUT TEMPERATURES REMAIN COLDER THAN NORMAL.
SUNDAY THROUGH TUESDAY...QUESTIONS REMAIN WHETHER THE POLAR JET
CONTINUES TO SUPRESS MOISTURE SOUTH OF THE REGION EARLY NEXT WEEK.
APPEARS THAT BRIEF RIDGING SHOULD OCCUR SUNDAY BEFORE THE NEXT COLD
FRONT APPROACHES BY MONDAY OR TUESDAY. GENERALLY FOLLOWED HPC.
&&
.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
THIS MORNING...
PERIOD OF HEAVY SNOW FOR MOST TERMINALS THIS MORNING TIL 15Z OR SO
THEN TRANSITIONING TO RAIN THEREAFTER. SEE TAFS FOR SPECIFICS. ALL
RAIN FOR HYA/FMH AND ACK.
REGARDING LOGAN/BOSTON...LOWERING TO IFR WITH RAIN BUT POSSIBLY
CHANGING BRIEFLY TO SNOW MID TO LATE MORNING IF WIND BACKS TO NORTH.
OTHERWISE MVFR LOWERING TO IFR AND POSSIBLY LIFR BY MIDDAY.
THIS AFTERNOON...LIFR IMPROVING TO IFR AS SNOW CHANGES TO SLEET THEN
RAIN FROM THE COAST TO INLAND AREAS AS E WINDS INCREASE. COULD SEE
WIND GUSTS CLOSE TO 50 KTS AT FMH/HYA AND ACK EARLY AFTERNOON. WINDS
WILL SHIFT TO S-SW LATE IN THE DAY.
OUTLOOK /TONIGHT THROUGH SUNDAY/...
TONIGHT THROUGH SUNDAY...VFR CONDITIONS. LOCAL MVFR IN -SHSN NEAR
THE BERKS THU PM THROUGH FRI PM. W WINDS GUSTING UP TO 35 TO 40 KT
AT TIMES THURSDAY THROUGH FRIDAY...PARTICULARLY ALONG THE SOUTH
COAST. WINDS DIMINISHING BY LATE SATURDAY. MECHANICAL WIND
SHEAR/TURBULENCE.
&&
.MARINE...
TODAY...
COASTAL LOW WILL PASS VICINITY OF CAPE COD CANAL THIS AFTERNOON
ACCOMPANIED BY A PERIOD OF EASTERLY STORM FORCE WINDS ACROSS
NANTUCKET AND CAPE COD WATERS. EASTERLY GALES ELSEWHERE.
POOR VSBY NEAR SHORE THIS MORNING ESPECIALLY NORTH OF CAPE COD
BAY...THEN IMPROVING IN RAIN LATE MORNING AND AFTERNOON.
OUTLOOK /TONIGHT THROUGH SUNDAY/...
TONIGHT THROUGH SATURDAY...HIGH PROBABILITY OF GALES THROUGH SATURDAY
AS EXCELLENT WIND MOMENTUM TRANSFER WILL CONTINUE DUE TO STRONG COLD
AIR ADVECTION OVER THE RELATIVELY WARM ATLANTIC WATERS. SHOULD SEE
GUSTS TO 35 TO 45 KT THROUGH SATURDAY...DIMINISHING TO SMALL CRAFT
BY LATE SATURDAY OR EARLY SUNDAY.
&&
.HYDROLOGY...
PRECIPITATION TOTALS /MOSTLY RAIN/ OF 1 TO 1.5 INCHES ARE POSSIBLE
ACROSS CT/RI AND SOUTHEAST MA AFTER THE CHANGEOVER FROM SNOW. WHILE THIS
MAY RESULT IN URBAN AND POOR DRAINAGE FLOODING...ESPECIALLY NEAR S
COAST...MAINSTEM RIVERS ARE EXPECTED TO REMAIN WITHIN THEIR BANKS.
&&
.TIDES/COASTAL FLOODING...
SE GRADIENT RAISES RISK OF MINOR COASTAL FLOODING ALONG MAINLY SE
FACING COASTLINES DURING THIS AFTERNOON HIGH TIDE. ETSS OUTPUT GIVES
ABOUT 1.5 FT ALONG THE MA E FACING COAST AND 2 TO 3 FT ALONG THE S
FACING COASTS OF RI AND BUZZARDS BAY. RECOGNIZING THAT THE SURGE FROM
THE ETSS TENDS TO BE CONSERVATIVE...WE HAVE ADDED A FEW TENTHS TO
HALF A FOOT TO THE MODEL VALUES. THE STRONGEST GRADIENT LOOKS TO
COINCIDE CLOSELY WITH THE TIME OF HIGH TIDE ALONG BOTH THE S COAST
AND E COAST OF MA...EVEN THOUGH THE HIGH TIDE TIMES THEMSELVES ARE
DIFFERENT.
WAVES OF 10 TO 15 FT NOT TOO FAR OFFSHORE WILL YIELD A SPLASH OVER
RISK ALONG THE EXPOSED COASTLINES. UPPER NARRAGANSETT BAY COULD GET
CLOSE TO MODERATE...SO A CHANCE THAT THE ADVISORY MAY HAVE TO BE
UPGRADED THERE. ONE SPECIAL CASE IS PROVINCETOWN HARBOR. WOULD NOT
EXPECT A SE WIND TO GENERATE MUCH SURGE THERE BUT ONCE THE WIND
SHIFTS TO SSW...THEN COULD SEE A SUDDEN SURGE OF PERHAPS 1.5 FEET OR
SO AND AN ONSHORE WIND FOR SPLASH OVER ALONG THE HARBOR FRONT.
ALSO HEAVY RAIN LATE THIS MORNING AND INTO THE AFTERNOON MAY
EXASCERBATE FLOODING IN THE UPPER PART OF NARRAGANSETT BAY /PROVIDENCE/
AND BOSTON HARBOR.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...WINTER STORM WARNING UNTIL 1 PM EST THIS AFTERNOON FOR
CTZ002>004.
MA...WINTER STORM WARNING UNTIL 1 PM EST THIS AFTERNOON FOR
MAZ002>006-008>014-026.
WIND ADVISORY UNTIL 3 PM EST THIS AFTERNOON FOR MAZ007-015-016-
018>021.
COASTAL FLOOD ADVISORY FROM 3 PM THIS AFTERNOON TO 7 PM EST
THIS EVENING FOR MAZ007-014>016-019-022.
WINTER WEATHER ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR
MAZ007-015>018.
COASTAL FLOOD ADVISORY FROM NOON TODAY TO 3 PM EST THIS
AFTERNOON FOR MAZ020-021.
HIGH WIND WARNING UNTIL 3 PM EST THIS AFTERNOON FOR MAZ022>024.
NH...WINTER STORM WARNING UNTIL 1 PM EST THIS AFTERNOON FOR NHZ011-
012-015.
RI...WINTER STORM WARNING UNTIL 1 PM EST THIS AFTERNOON FOR RIZ001.
WIND ADVISORY UNTIL 3 PM EST THIS AFTERNOON FOR RIZ006>008.
WINTER WEATHER ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR
RIZ002>005.
COASTAL FLOOD ADVISORY FROM NOON TODAY TO 3 PM EST THIS
AFTERNOON FOR RIZ002-004>007.
MARINE...STORM WARNING UNTIL 5 PM EST THIS AFTERNOON FOR ANZ231-232-250-
254-255.
GALE WARNING UNTIL 5 PM EST THIS AFTERNOON FOR ANZ230-233>237-
251-256.
&&
$$
SYNOPSIS...STRAUSS
NEAR TERM...NOCERA
SHORT TERM...STRAUSS
LONG TERM...STRAUSS
AVIATION...NOCERA/STRAUSS - UPDATED 633 AM
MARINE...NOCERA/STRAUSS
HYDROLOGY...NOCERA
TIDES/COASTAL FLOODING...NOCERA
