Winter Storm Watch 3, NWS Boston/Norton, MA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TAUNTON MA
351 PM EST WED FEB 28 2007

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...

MAIN FORECAST CHALLENGE IN THE SHORT TERM PERIOD REVOLVES AROUND
PRECIP TYPE AND INTENSITY FOR THURSDAY NIGHT.

IN THE MEANTIME...FOR TONIGHT...EXPECT MOSTLY CLEAR SKIES. TOOK A
BLEND OF THE MOS VALUES FOR MINS. INCREASING CLOUDS ARE EXPECTED ON
THURSDAY AS A LOW PRESSURE SYSTEM APPROACHES FROM THE WEST. EXPECT
HIGHS NEAR NORMAL DURING THE DAY THURS.

WARM AIR ADVECTION REALLY GETS CRANKING THURSDAY EVENING AS A STRONG
SOUTHERLY LOW LEVEL JET DEVELOPS IN ADVANCE OF APPROACHING SHORT
WAVE TROF. THIS WILL RESULT IN PRECIPITATION QUICKLY OVERSPREADING
SOUTHERN NEW ENGLAND. IT WILL DEVELOP FIRST IN THE WESTERN ZONES
EARLY IN THE EVENING...THEN PROGRESS EASTWARD TO THE FAR EASTERN
SECTIONS OF THE CWA BY MIDNIGHT. THE PRECIPITATION WILL BECOME HEAVY
AT TIMES OWING TO VERY STRONG ISENTROPIC UPGLIDE IN THE 285K TO 300K
LAYER.

THE QUESTION THEN BECOMES PRECIPITATION TYPE. GIVEN THE STRENGTH OF
THE LOW LEVEL JET AND THE LOW AND MID LEVEL TROF AXIS REMAINING TO
THE WEST...THINKING THAT LOCATIONS ROUGHLY ALONG AND SOUTH OF ROUTE
2 WILL EXPERIENCE A FAIRLY BRIEF PERIOD OF SNOW THURSDAY
NIGHT...WHICH WILL QUICKLY CHANGE TO A MIXTURE OF SNOW/SLEET/RAIN
AND POSSIBLY FREEZING RAIN BEFORE RUSH HOUR FRIDAY MORNING. NOT
EXPECTING MUCH IN THE WAY OF SNOW ACCUMULATION IN THESE
AREAS...PERHAPS A QUICK 1 TO 2 INCHES SOUTH OF THE MASS PIKE AND 2
TO 4 INCHES BETWEEN THE MASS PIKE AND ROUTE 2. ALONG AND SOUTH OF
I-95...INCLUDING NORTHERN CT...EXPECT VERY LITTLE IN THE WAY OF SNOW
ACCUMULATIONS AS CHANGEOVER TO SLEET/RAIN SHOULD OCCUR QUITE QUICKLY.

FOR NORTHWESTERN MASS...INCLUDING SOUTHERN NEW HAMPSHIRE...WE FEEL
THAT 3 TO 6 INCHES OF SNOW WILL BE POSSIBLE BEFORE A CHANGEOVER TO
SLEET AND FREEZING RAIN OCCURS. HOWEVER...BECAUSE OF THE COMBINATION
OF SNOW...SLEET...AND FREEZING RAIN THAT IS FORECAST TO OCCUR ON TOP
OF THE 3 TO 6 INCHES OF SNOW DURING THE RUSH HOUR FRIDAY
MORNING...HAVE OPTED TO GO WITH A WINTER STORM WATCH FOR THURSDAY
NIGHT THROUGH NOON FRIDAY. HAVE INCLUDED THE FOLLOWING COUNTIES OR
PORTIONS OF COUNTIES IN MASSACHUSETTS: EXTREME NORTHWEST
MIDDLESEX...NORTHERN WORCESTER...FRANKLIN...HAMPSHIRE. IN SOUTHERN
NEW HAMPSHIRE...ALL OF HILLSBOROUGH AND ALL OF CHESHIRE.
&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
FRIDAY...
A MIX OF SNOW/SLEET AND FREEZING RAIN ACROSS NORTHWEST MA AND
SOUTHWEST NH WILL BE WINDING DOWN AROUND MIDDAY...AS DRY SLOT MOVES
ACROSS THE AREA FROM WEST TO EAST. FARTHER SOUTH...MAIN CONCERN WILL
BE HEAVY RAIN POTENTIAL AS STRONG LOW LEVEL JET COMBINES WITH DEEP
LAYER MOISTURE WITH PWS CLIMBING TO +1.0.

GFS IS FARTHER S WITH AXIS OF HEAVY RAIN...WHICH IS CENTERED ALONG
SOUTH COAST...WITH NAM FARTHER N ACRS CT/RI AND MUCH OF MA ALONG AND
SOUTH OF THE MASS PIKE. GGEM FARTHER NORTHWEST LIKE THE NAM. A LOT
OF CENTERS AROUND THE TRACK OF SURFACE LOW AND ITS ASSOCIATED
CONVERGENCE FIELD AND LOW LEVEL MOISTURE/THERMAL ADVECTION. GIVEN
TRACK OF MID LEVEL DYNAMICS TRACK WELL NORTHWEST OF THE
REGION...THINK SURFACE LOW AND QPF WILL TRACK FARTHER NORTHWEST
ACROSS CT/RI AND MUCH OF MA PER THE NAM AND GGEM.  THIS SURFACE LOW
TRACK WILL ALSO PROVIDE SOME OROGRAPHIC ENHANCEMENT TO THE QPF
ACROSS HILLY TERRAIN OF CT AND MA.

LATER SHIFTS WILL HAVE TO MONITOR POTENTIAL FOR POOR DRAINAGE/URBAN
FLOODING FRI MORNING....WHICH WOULD IMPACT THE MORNING COMMUTE.

REGARDING WINDS FRI...LOW RISK OF STRONG TO DAMAGING WINDS CAPE COD
AND ISLANDS GIVEN STRENGTH (60KT AT 925 AND 80 KT AT 850MB) OF LOW
LEVEL JET. HOWEVER LOCAL STUDY FOR SOUTHEAST WIND CASES INDICATES
STRENGTH OF LOW LEVEL JET NEEDS TO BE ABOUT 10-15 KT STRONGER. IN
ADDITION...COLD NEAR SHORE WATERS WITH SST IN THE 30S COMBINED WITH
STRONG WAA ON THE NOSE OF LOW LEVEL JET WILL CREATE A STEEP
INVERSION. THUS...MIXING/GUSTINESS WILL BE LIMITED. HOWEVER...MODEL
SOUNDINGS FROM BOTH THE NAM AND GFS INDICATE A LOW RISK OF
GRADIENT/SUSTAINED WIND REACHING WARNING CRITERIA /35 KT/ ACROSS
CAPE COD AND THE ISLANDS. MORE LIKELY SCENARIO WOULD BE HIGH END
WIND ADVISORY WITH WINDS OF 30-40 MPH...MAINLY SUSTAINED WINDS.

FRIDAY NIGHT...
COLUMN DRIES OUT IN RESPONSE TO SHORT WAVE RIDGING OVER THE AREA
BEHIND DEPARTING INITIAL WAVE. THUS...DRY WEATHER EXPECTED.

SATURDAY...
SHOWERS POSSIBLE...MAINLY IN THE AFTERNOON ACROSS WESTERN PORTIONS
OF CT/MA AND NH AS TRAILING SHORT WAVE TROF ALONG WITH WEAK SURFACE
REFLECTION MOVES ACROSS THE AREA.

SUNDAY THROUGH WEDNESDAY...
DRY AND COOL CYCLONIC FLOW SUNDAY AND MONDAY...WITH NEAR SEASONABLE
TEMPS. BIG DILEMMA IS FOR TUE...AS MODELS RELOAD JET ENERGY INTO
NORTHEAST/SOUTHEAST CANADA TROF WITH COLD FRONTAL PASSAGE LATE
MON/MON NIGHT. 00Z ECMWF WAS MOST BULLISH WITH COLD SURGE...LIMITING
HIGHS TUE IN THE 20S HOWEVER...12Z RUN HAS BACKED OFF AND IS
SLIGHTLY WARMER. 12Z GFS REMAINS FLATTEST HERE...WITH 12Z GGEM IN
BETWEEN. THEREFORE...WE WILL FOLLOW A MODEL BLEND WHICH WILL BE
SLIGHTLY COOLER THAN MEX GUID BUT WARMER THAN HPC GUID.

BY WED...TEMPS MODERATE AS UPPER FLOW BECOMES MORE ZONAL.

&&

.AVIATION...
VFR CONDITIONS EXPECTED OVERNIGHT TONIGHT THROUGH 18Z ON THURSDAY.
ANY BROKEN STRATOCU WILL DISSIPATE BY EARLY THIS EVENING.
&&

.MARINE...
RELATIVELY TRANQUIL WINDS AND SEAS ARE EXPECTED ON THE LOCAL WATERS
TONIGHT THROUGH MOST OF THURS NITE. LOW PRESSURE WILL APPROACH FROM
THE WEST THURSDAY NIGHT WHICH COULD ALLOW FOR SMALL CRAFT OR GALE
FORCE WINDS BY DAYBREAK FRIDAY. HOWEVER...THIS IS VERY LATE 3RD
PERIOD OF THE FORECAST SO HAVE HELD OFF ON ANY FLAGS ATTM.

FRIDAY...
SOUTHEAST WINDS MAY APPROACH GALE FORCE...THEN DIMINISH AND BECOME
SOUTHWEST FRI EVENING AND NIGHT.

SAT...MODEST SOUTHWEST WINDS.

SUN AND MON...MODEST WEST WINDS WITH A LOW RISK OF WEST-NORTHWEST
GALES LATE MON NIGHT...AS STRONG COLD FRONT MOVES ACROSS NEW
ENGLAND.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...NONE.
MA...WINTER STORM WATCH FROM THURSDAY EVENING THROUGH FRIDAY
     MORNING FOR MAZ002>004-008-010-026.

NH...WINTER STORM WATCH FROM THURSDAY EVENING THROUGH FRIDAY
     MORNING FOR NHZ011-012-015.

RI...NONE.
MARINE...NONE.
&&

SHORT TERM...EKSTER
LONG TERM...NOCERA
AVIATION...EKSTER
MARINE...NOCERA/EKSTER

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