FXUS61 KBOX 050955
AFDBOX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
455 AM EST SAT DEC 5 2009

.SYNOPSIS...
LOW PRESSURE DEVELOPING OFF THE SOUTHEAST COAST THIS MORNING WILL
MOVE RAPIDLY NORTHEASTWARD TODAY AND PASS SOUTHEAST OF NANTUCKET
TONIGHT. THIS SYSTEM SHOULD GIVE A GOOD PORTION OF SOUTHERN NEW
ENGLAND IT/S FIRST SIGNIFICANT SNOWFALL OF THE SEASON. THIS LOW WILL
QUICKLY MOVE AWAY ON SUNDAY AND BE REPLACED BY HIGH PRESSURE THROUGH
MONDAY. WEAK LOW PRESSURE MAY AFFECT SOUTHERN NEW ENGLAND MONDAY
NIGHT. MORE SIGNIFICANT LOW PRESSURE LOOKS TO IMPACT THE REGION
MIDWEEK WITH A MIXTURE OF PRECIPITATION AND WIND.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
LOW PRESSURE WILL MOVE UP THE EAST COAST TODAY AND TONIGHT AND SHOULD
DELIVER SOUTHERN NEW ENGLANDS FIRST SIGNIFICANT SNOWFALL OF THE
SEASON. HOWEVER...THERE ARE SEVERAL FACTORS INVOLVED THAT MAKE THIS A
LESS THAN HIGH CONFIDENCE FORECAST. MUCH OF THE FORECAST WAS DERIVED
FROM A BLEND OF THE NAM/GFS/ECMWF WITH SEVERAL ADJUSTMENTS MADE TO QPF
AND TEMPS. THE MAIN CONCERNS REVOLVE AROUND BOUNDARY LAYER
TEMPERATURES...AS WELL AND WHERE EXACTLY THE HEAVIEST PRECIPITATION
WILL FALL AND WHEN. IT APPEARS AS THOUGH THE MAIN ACTION WILL BEGIN
LATER THIS AFTERNOON AND ESPECIALLY THIS EVENING.

LIGHT PRECIPITATION SHOULD BEGIN TO OVERSPREAD SOUTHERN NEW ENGLAND
FROM SOUTH TO NORTH BY LATE MORNING. MUCH OF THIS PRECIPITATION WILL
BE IN THE FORM OF RAIN DUE TO RELATIVELY WARM TEMPERATURES AT AND
NEAR THE SURFACE. HOWEVER...HIGHEST ELEVATIONS OF THE INTERIOR MAY
START AS SNOW OR A RAIN SNOW MIX. AS HEAVIER PRECIPITATION DEVELOPS
OVER THE REGION THIS AFTERNOON...SNOW LEVELS WILL DROP AND ALLOW FOR
SNOW TO BEGIN ACCUMULATING AT HIGHER ELEVATIONS. THE COASTAL PLAIN
AND OTHER LOWER ELEVATION LOCATIONS WILL LIKELY REMAIN ALL RAIN
THROUGH THE AFTERNOON UNTIL GREATER VALUES OF UPWARD VERTICAL MOTION
ARRIVE...WHICH SHOULD BE TOWARD EVENING OR DURING THE EVENING. OF
COURSE...THE TIMING COULD VARY A BIT...SO ATTENTION WILL HAVE TO BE
PAID TO SUBSEQUENT FORECAST UPDATES. A VERY CHANGEABLE WEATHER
SITUATION WILL LIKELY DEVELOP TODAY...IT MAY TAKE A SHORTER AMOUNT OF
TIME FOR SOME LOCATIONS TO FLIP TO SNOW...WHILE IT TAKES A BIT LONGER
AT OTHERS DUE TO MESOSCALE ASCENT DISTRIBUTION.

WE HAVE ISSUED WINTER WEATHER ADVISORIES FOR THE WESTERN AND CENTRAL
PORTIONS OF THE FORECAST AREA STARTING MID AFTERNOON.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
A WINTER WEATHER ADVISORY IS IN EFFECT FOR MUCH OF SOUTHERN NEW
ENGLAND FOR TONIGHT...EXCEPT FOR SOUTHERN NH AND IMMEDIATE COASTAL
LOCATIONS OF SE MASS AND RI. UPWARD VERTICAL MOTION SHOULD BE
CRANKING PRETTY GOOD BETWEEN 00Z AND 06Z. THIS WILL RESULT IN A
TRANSITION FROM RAIN TO SNOW FROM WEST TO EAST...AND IT MAY OCCUR
VERY QUICKLY BETWEEN 00Z AND 03Z ON THE COASTAL PLAIN AS LONG AS
STRONG OMEGA DEVELOPS. THE EXACT AMOUNT OF SNOWFALL WILL DEPEND ON
QPF...WHERE THE BEST OMEGA ENDS UP BEING...AND THE TEMPERATURE
PROFILES.

SOME OF THE GUIDANCE IS TRYING TO CLOSE OFF THE MID LEVEL LOW FOR A
TIME THIS EVENING...AND THIS MAY INCREASE SNOWFALL RATES QUITE
STOUTLY AS MESOSCALE BANDING TRIES TO TAKE SHAPE...ESPECIALLY ACROSS
EASTERN ZONES. THIS COULD ADD A BIT MORE TO SNOWFALL TOTALS THERE.
FOR NOW...WE THINK THE HIGHER ELEVATIONS OF CENTRAL MASS AND CT WILL
DO BEST IN TERMS OF SNOW...BUT THIS IS THE TYPE OF SYSTEM THAT COULD
THROW A FEW CURVEBALLS. AT THIS TIME...WE ARE FORECASTING A GENERAL 2
TO 5 INCHES OF SNOWFALL...WITH 3 TO 6 IN THE HIGHER ELEVATIONS. IF
MESOSCALE BANDING WERE TO GET GOING THIS EVENING...THEN HIGHER
SNOWFALL TOTALS COULD BE EXPECTED...EVEN ON THE COASTAL PLAIN.
EASTERN MASS/INTERIOR SE MASS/RHODE ISLAND LOOK PARTICULARLY
INTRIGUING WITH RESPECT TO THE POTENTIAL FOR MESOSCALE BANDING AND
WE/LL HAVE TO KEEP AN EYE OUT FOR THAT THIS EVENING. COASTAL FRONT
ENHANCEMENT MAY BE ANOTHER FACTOR TO CONSIDER AS WELL. THERE/S A LOW
PROB THAT SOMEONE SEES LOW-END WINTER STORM WARNING CRITERIA SNOWFALL
OUT OF THIS...BUT THOSE AREAS ARE TOO DIFFICULT TO PINPOINT AT THIS
TIME. IN ADDITION...SOUTHERN NEW HAMPSHIRE ISN/T COMPLETELY OUT OF
THE WOODS. THEIR ADVISORY CRITERIA IS A BIT HIGHER THAN THE REST OF
SNE SO DIDN/T ISSUE ONE AT THIS TIME...BUT THEY MAY NEED TO BE
UPGRADED LATER IF IT LOOKS FOR CERTAIN THAT HIGHER QPF VALUES WILL
MAKE IT UP THERE.

SNOW MAY FALL HEAVY AT TIMES THIS EVENING. SINCE THE BOUNDARY LAYER
TEMPERATURES WILL BE NEAR FREEZING...SNOW MAY ACCUMULATE ON TREES AND
WIRES CAUSING BRANCH BREAKAGE AND THE POTENTIAL FOR SCT POWER OUTAGES.

NORTHERLY WINDS WILL BECOME AN ISSUE ON THE CAPE AND ISLANDS WITH
GUSTS UP TO 50-55 MPH POSSIBLE AS THE STORM CONTINUES TO INTENSIFY.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
ACTIVE PATTERN CONTINUES INTO NEXT WEEK. LEFT OVER SNOW SHOWERS MAY 
LINGER UNTIL 13Z OR 14Z OVER THE CAPE AND NANTUCKET. OTHERWISE...BECOMING
MOSTLY SUNNY AND BLUSTERY ON SUN. EXPECT MON TO START OUT DRY BUT
THEN BECOME MOSTLY CLOUDY WITH CHANCE SNOW SHOWERS ACROSS NORTHERN
ZONES AS SHORT WAVE TROF RAPIDLY APPROACHES IN FAST ZONAL FLOW. THERE
MAY BE A WEAK SURFACE LOW OR TROUGH REFLECTION MON EVENING.

LOOKS LIKE ENOUGH MOISTURE AND DYNAMICS TO WARRANT A LOW CHANCE OF
SNOW SHOWERS IN NORTHERN ZONES FOR MON EVE. THIS APPROACH SUPPORTED BY
SREF .01 PROB.

CONSIDERABLE COLD AIR IN PLACE AHEAD OF NEXT SIGNIFICANT EVENT WED 
AND WED NIGHT WHEN EXPECT STRONG OVERRUNNING AND START OF PRECIPITATION AS
SNOW MOST LOCATIONS. MOST MEDIUM RANGE MODEL OUTPUT BRINGS PRIMARY
SURFACE LOW ACROSS EASTERN GREAT LAKES WITH DEVELOPING TRIPLE POINT
LOW THAT TRACKS RIGHT ACROSS SOUTHERN NEW ENGLAND. LOW LEVEL JET OF
60+ KT FROM SE ACROSS TIGHT TEMPERATURE GRADIENT ACCOMPANIED BY
SUBTROPICAL SOURCE OF MOISTURE WILL LIKELY PRODUCE COPIOUS AMOUNTS OF
PRECIPITATION. ATTM...THINKING THERE WILL BE A BURST OF
SNOW...PERHAPS A FEW INCHES ON THE FRONT END AND THEN A CHANGE TO
SLEET/FREEZING RAIN AND THEN MOSTLY RAIN. MAY HAVE A MORE SIGNIFICANT
SNOW ACCUMULATION ACROSS SW NH...AND IF TRIPLE LOW FAR ENOUGH
EAST...THEN LOW LEVEL COLD AIR COULD HANG IN AND CAUSE A SNOW TO
SLEET TO FREEZING RAIN SCENARIO ACROSS SW NH AND NW MA. HAVE CAPPED
POPS AT LIKELY CATEGORY DUE TO LENGTH OF TIME BEFORE MID WEEK EVENT
AND INHERENT UNCERTAINTY WITH SUCH LEAD TIMES. ALSO HELD BACK THE
ONSET A LITTLE SINCE EXPECT A LOT OF LOW LEVEL DRY AIR THAT WILL NEED TO
BE OVERCOME AT THE OUTSET.

THERE IS A CHANCE THAT SOUTH WINDS MAY REACH WIND ADVISORY CRITERIA 
OVER THE CAPE AND ISLANDS SOMETIME WED NIGHT...BUT THIS DEPENDS ON
DETAILS THAT ARE HARD TO RESOLVE THIS FAR OUT.

A SHIFT IN THE TRACK AND TIMING OF TRANSFER OF ENERGY TO SECONDARY
LOW COULD RESULT IN FAIRLY DRAMATIC CHANGES TO THE FORECAST...
ESPECIALLY WITH REGARD TO PTYPE AND WIND THREATS.

WE TURN COLD AGAIN AFTER THE MID WEEK EVENT. KEPT CHANCE POPS GOING 
IN NORTHERN ZONES ON THU UNTIL THE PASSAGE OF THE UPPER TROF.

&&

.AVIATION /10Z SATURDAY THROUGH WEDNESDAY/...
TODAY AND TONIGHT...MVFR CIGS SPREAD S TO N DURING THE DAY TIME
FRAME WITH RAIN DEVELOPING. CONDS LOWER FURTHER IN THE AFTN...TO IFR
CONDITIONS BY EARLY EVENING. LATE AFTERNOON PRECIP GENERALLY -RA IN
TAF LOCATIONS BUT MIX/CHANGEOVER TO -SN W OF BOS/PVD PRIOR TO 00Z. A
PERIOD OF MODERATE SNOWFALL IS POSSIBLE AT ALL TAF SITES THIS EVENING
AS LOW PRESSURE MAKES IT/S CLOSEST APPROACH. CONDITIONS WILL LIKELY
BE IFR TO VLIFR FOR A TIME THIS EVENING. IMPROVEMENT IS FORESEEN FROM
WEST TO EAST...STARTING AT 03Z IN THE WEST...AND 06Z-08Z IN THE EAST.

NNE GUSTS 30-40 KTS LIKELY CAPE COD AND THE ISLANDS TONIGHT.

OUTLOOK /SUNDAY THROUGH THURSDAY/...

SUN...MVFR CIGS POSSIBLE EARLY BOS TO HYA TO ACK...THEN VFR ALL
AREAS. SFC WIND GUSTS 20 TO 25 KT MAY CAUSE MECHANICAL TURBULENCE.
MON...VFR...EXCEPT AREAS OF MVFR POSSIBLE DURING MON EVENING IN SCTD
-SHRA/-SHSN. 
TUE...VFR. 
WED...POTENTIAL FOR IFR AND STRONG WINDS. 
THU...BECOMING MOSTLY VFR BUT STRONG WINDS.

&&

.MARINE...
GALE WARNINGS HAVE BEEN POSTED FOR ALL WATERS EXCEPT FOR BOSTON
HARBOR AND NARRAGANSETT BAY...BUT IT/S POSSIBLE THAT THOSE TWO
LOCATIONS MAY BE ADDED LATER. OVERALL...COASTAL STORM PASSES
SOUTHEAST OF NANTUCKET TONIGHT. WINDS AND SEAS INCREASE TO GALE AS
THE AFTERNOON PROGRESSES...WITH THE STRONGEST GUSTS...POSSIBLY 45
KT...OVERNIGHT TONIGHT. SEAS WILL BECOME VERY ROUGH.

OUTLOOK /SUNDAY THROUGH THURSDAY/...
EXPECT LEFTOVER HAZARDOUS SEAS ON SUN AND GALE FORCE WINDS EARLY.
WIND DIMINISHES LATE IN DAY AND SEAS SUBSIDING SUN NIGHT. INCREASING
SE WIND WILL REQUIRE AT LEAST SMALL CRAFT ADVISORY HEADLINE IF NOT
GALE WARNING FOR SOUTH COASTAL WATERS ON WED. NW GALE LIKELY ON BACKSIDE
OF SURFACE LOW FOR THU.

&&

.TIDES/COASTAL FLOODING...
NE TO N WIND COULD BRING A 1 TO 1.5 SURGE TO SANDWICH AND OTHER 
NORTH AND NE FACING CAPE COD BAY SHORELINES LATE TONIGHT BUT EXPECT
ONLY SPLASHOVER AT WORST AS THE NIGHTTIME ASTRO TIDE IS NOT
ESPECIALLY HIGH. SHOULD BE LOSING ONSHORE FLOW COMPONENT OF WIND BY
THE TIME OF THE HIGHER SUN AFTERNOON ASTRO TIDE.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...WINTER WEATHER ADVISORY FROM 3 PM THIS AFTERNOON TO 7 AM EST 
     SUNDAY FOR CTZ002>004.
MA...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST 
     SUNDAY FOR MAZ005>007-013>018.
     WINTER WEATHER ADVISORY FROM 3 PM THIS AFTERNOON TO 7 AM EST 
     SUNDAY FOR MAZ002>004-008>012-026.
     WIND ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST SUNDAY FOR 
     MAZ022>024.
NH...NONE.
RI...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 AM EST 
     SUNDAY FOR RIZ001>004-006.
MARINE...GALE WARNING FROM 5 PM THIS AFTERNOON TO 7 AM EST SUNDAY FOR 
     ANZ231>235-237-250-251-254>256.
     SMALL CRAFT ADVISORY FROM 5 PM THIS AFTERNOON TO 7 AM EST 
     SUNDAY FOR ANZ230-236.

&&

$$
SYNOPSIS...EKSTER
NEAR TERM...EKSTER
SHORT TERM...EKSTER
LONG TERM...THOMPSON
AVIATION...EKSTER/THOMPSON
MARINE...EKSTER/THOMPSON
TIDES/COASTAL FLOODING...THOMPSON