NWS - major winter storm ahead

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...

NASTY LATE SEASON NOREASTER WILL AFFECT SOUTHERN NEW ENGLAND FRIDAY
INTO EARLY SATURDAY. THE GENERAL OVERALL SETUP DOESN'T ACTUALLY LOOK
ALL THAT DISSIMILAR FROM THE VALENTINES DAY STORM...BUT WE THINK
SNOWFALL TOTALS WILL BE HIGHER OVER EASTERN SECTIONS OF THE CWA THIS
TIME AROUND.

THERE ARE SEVERAL THINGS TO CONSIDER HERE...INCLUDING SNOW/MIXED
PRECIP AMOUNTS...WINDS...FLOODING FROM RAINFALL...AS WELL AS THE
POSSIBILITY FOR SOME COASTAL FLOODING.

WE LIKED THE CONSENSUS OF THE 00Z OPERATIONAL GFS AND 00Z
GGEM FOR LOW TRACK OVER SOUTHEAST MASS EARLY SATURDAY. GFS ENSEMBLE
MEAN IS VERY CLOSE TO THIS TRACK...BUT PERHAPS A TAD EAST...AND WE
KEPT THIS IN MIND.

OVERALL...WE LIKED THE CONFIGURATION OF THE GOING WINTER STORM
WATCHES...AND HAVE KEPT THE COUNTIES PREVIOUSLY INCLUDED. WE HOWEVER
DID ADJUST THE TIMING BIT SINCE IT DOES LOOK LIKE THE START OF THE
ACCUMULATING SNOW WILL BE EARLY FRIDAY MORNING...SO PUSHED BACK THE
START TIME OF THE WATCH FOR FRIDAY MORNING INSTEAD OF TONIGHT.

LOW PRESSURE WILL BEGIN TO INTENSIFY OVER THE SOUTHEAST STATES
FRIDAY MORNING AS LARGE AND POTENT SHORT WAVE APPROACHES THE
APPALACHIANS. THE LOW WILL THEN MOVE UP THE COAST FRIDAY NIGHT AND
SATURDAY...CROSSING SOUTHEAST MASS EARLY SATURDAY MORNING.

FRONTAL BOUNDARY THAT SINKS TO THE SOUTH OF NEW ENGLAND TODAY WILL
PARK ITSELF OFFSHORE WELL TO OUR SOUTH TONIGHT...AND THIS BOUNDARY
WILL SERVE AS AN EXCELLENT MECHANISM TO AID IN THE EXPLOSION OF
OVERRUNNING PRECIPITATION BY EARLY SATURDAY MORNING. AS THE AREA OF
LOW PRESSURE INTENSIFIES AND MOVES UP THIS FRONT...THE BAROCLINIC
ZONE WILL TIGHTEN WHICH WILL AID IN INCREASING FRONTOGENESIS THROUGH
THE LOW AND MID LEVELS AS FRIDAY AND FRIDAY NIGHT PROGRESSES.

EXPECT SNOW TO OVERSPREAD ALL OF SOUTHERN NEW ENGLAND FROM SOUTH TO
NORTH FRIDAY MORNING...STARTING BY/AROUND RUSH HOUR OVER CT/RI/SE
MASS...THEN SPREADING NORTHWARD AND REACHING NORTHERN ZONES BY MID
TO LATE MORNING. INCREASING LOW AND MID LEVEL FRONTOGENESIS...DECENT
DENDRITIC GROWTH PROFILES...AND THE POTENTIAL FOR SOME CSI /BASED ON
GFS X-SXNS/ INDICATE THAT THE SNOW WILL LIKELY BE HEAVY AT TIMES.

BY FRIDAY AFTERNOON...WARMER AIR WILL BEGIN TO INVADE FROM THE SOUTH
ON A STRENGTHENING LOW LEVEL JET AS 750-800 MB LAYER WARM FRONT
SURGES NORTHWARD. THIS WILL ALLOW FOR A GRADUAL CHANGEOVER TO MIXED
PRECIPITATION FROM SOUTH TO NORTH MAINLY DURING THE AFTERNOON AND
EVENING FRIDAY. THE SOUTH COAST WILL OBVIOUSLY SEE THE CHANGE
FIRST...PROBABLY BY LATE MORNING...SO THEIR SNOW ACCUMS WILL BE
LIMITED. IN FACT...THE ISLANDS MAY NOT SEE ANY SNOW AT ALL. MOST OF
THE CWA WILL PROBABLY BE SEEING MIXED PRECIP BY MIDNIGHT...WITH MOST
IF NOT ALL OF EASTERN MASS SEEING A CHANGE TO PLAIN RAIN DURING THE
NIGHT. SEE HYDROLOGY SECTION FOR MORE INFO ON EXPECTED RAINFALL
IMPACTS. WESTERN MASS AND SOUTHWEST NH MAY NOT MIX AS THEY WILL BE
ALONG OR JUST WEST OF THE LOW/MID LEVEL LOW.

DRY SLOT QUICKLY APPROACHES EARLY SATURDAY MORNING...AND THIS
WILL EFFECTIVELY END ANY STEADY PRECIPITATION DURING THE MORNING
HOURS.

WITH ALL THIS SAID...THERE WILL LIKELY BE A PRETTY IMPRESSIVE THUMP
OF SNOW FOR MOST EVERYONE EXCEPT THE SOUTH COAST/CAPE/ISLANDS GIVEN
SAID METEOROLOGICAL FACTORS. BEFORE ANY MIX/CHANGEOVER TO
RAIN...CURRENT THINKING IS THAT 10 TO 16 INCHES OF SNOW WILL FALL TO
THE NORTHWEST OF A HARTFORD CT - LAWRENCE MASS LINE WITH THE
GREATEST AMOUNTS OF THE RANGE OVER WESTERN MASS AND SW NH. TO THE
SOUTHEAST OF THIS LINE...SNOWFALL AMOUNTS WILL DECREASE AS ONE HEADS
TOWARD THE COAST...BUT AT THIS TIME WE'RE STILL EXPECTING LOW-END
WINTER STORM WARNING CRITERIA TO BE MET FOR THE I-95 CORRIDOR FROM
THE NORTHERN SUBURBS OF PROVIDENCE TO BOSTON. TO THE SOUTHEAST OF
THERE...SNOW AMOUNTS WILL BE CONSIDERABLY LESS DUE TO THE QUICKER
INFLUX OF WARM AIR.

WITH THIS SAID...THE EXACT TRACK OF THE LOW PRESSURE SYSTEM WILL
ULTIMATELY DETERMINE SNOWFALL AMOUNTS. A FAST FASTER INFLUX OF WARM
AIR COULD CUT DOWN ON SNOW AMOUNTS AS WELL. NOTHING IS SET IN STONE
AT THIS JUNCTURE.