HPC & Boston Discussion
Posted by JAC on 1/10/2011, 8:24 am
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
314 AM EST MON JAN 10 2011

VALID 12Z MON JAN 10 2011 - 12Z THU JAN 13 2011


DAYS 2 AND 3...

MIDWEST TO MID ATLC/NORTHEAST...
BROAD CENTRAL U.S. UPPER SYSTEM SPREADS EWD AND EVENTUALLY CLOSES
OFF A 5H CENTER FROM OH TO THE MID ATLC AREA.  BATCH OF MDT SNOW
WILL ACCOMPANY THE STRONG UPPER FORCING AND WEAK SFC FEATURE FROM
THE OH VALLEY AREA TO PA.  A MUCH STRONGER AND RAPIDLY
INTENSIFYING SFC LOW IS PROGGED TO LIFT NNE FROM NEAR CAPE
HATTERAS TUES NIGHT.  THIS SYSTEM WILL BRING A PERIOD OF STRONG
ATLC INFLOW WITH HVY SNOW INTO PARTS OF THE MID ATLC TO SRN NEW
ENG.  THE CONSISTENT ECMWF SOLN WAS LARGELY PREFERRED WITH THE
TRACK OF THIS SYSTEM...WHICH PLACES LOCATIONS FROM NJ TO MA IN
LINE FOR A SIGNIFICANT SNOWFALL ALONG WITH STRONG WINDS.  BL TEMPS
MAY WARM ENOUGH FOR SOME RAIN ALONG PORTIONS OF THE COAST
ESPECIALLY ACROSS CAPE COD AND THE ISLANDS.  MODEL DIFFS ARE STILL
LARGE WITH SEVERAL MODELS INDICATING FARTHER OFFSHORE
SOLNS...WHILE THE NAM IS A WESTERN OUTLIER.  MOST MODELS PUSH THE
CIRCULATION FAR ENOUGH EAST ON DAY 3 TO LIMIT THE NRN EXTENT OF
MDT SNOW TO THE COASTAL AREAS OF MAINE.



NATIONAL WEATHER SERVICE TAUNTON MA
615 AM EST MON JAN 10 2011


LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...

-- Changed Discussion --TUESDAY NIGHT AND WEDNESDAY...MEDIUM RANGE CONSENSUS CONTINUES FOR
MOST MODELS IN BRINGING THE COASTAL STORM CLOSE TO OR JUST INSIDE
THE 40N/70W BENCHMARK DURING THIS TIMEFRAME. THE 00Z GFS ENSEMBLE
MEANS ALSO CLUSTER THE CENTER OF THE STORM RIGHT AROUND THE
BENCHMARK AT 12Z WED.

WITH THE MAJORITY OF MODEL RUNS OVER THE LAST COUPLE OF DAYS
SIGNALING THIS BENCHMARK TRACK...ALONG WITH OUR KNOWN CLIMATOLOGY
FOR MAJOR EFFECTS FROM STORMS PASSING ON THIS TRACK...IT IS TIME TO
START GIVING MORE DETAILS ABOUT WHAT WE THINK WILL HAPPEN WITH THIS
SYSTEM.

FIRST OF ALL...WE HAVE ISSUED A WINTER STORM WATCH FOR MOST OF OUR
COUNTY WARNING AREA. OUR FORECASTED QPF AMOUNTS ARE ON THE ORDER OF
0.7 INCHES ACROSS SW NH INTO NW MA...UP TO 1-1.25 INCHES ACROSS
EASTERN AND CENTRAL MA...RI AND E CT. VERY DYNAMIC SYSTEM AS THE LOW
UNDERGOES BOMBOGENESIS OVERNIGHT TUESDAY AND WEDNESDAY MORNING.
WOULD NOT BE SURPRISED TO SEE SOME SLANTWISE VORTICITY THAT COULD
CAUSE SOME THUNDER SNOW AS WELL. PLUS...WILL LIKELY SEE SNOW BANDING
WITH LOCALLY HEAVY SNOWFALL. EXCELLENT DENDRITIC GROWTH IN PLACE
WITH VERY STRONG LIFT ACROSS MOST OF THE REGION. ALL THIS ADDS UP TO
SUBSTANTIAL SNOWFALL FOR A GOOD MAJORITY OF THE REGION. HAVE ISSUED
OUR FIRST EARLY FORECAST FOR SNOW AMOUNTS ON OUR WEBSITE. WITH
INCREASING NE WINDS OVERNIGHT...EXPECT TEMPS ON THE OUTER CAPE AND
NANTUCKET TO BE MARGINAL FOR HEAVY SNOWFALL...SO EXPECT LOWER
AMOUNTS THERE. OTHERWISE...IT DOES LOOK LIKE EVEN THE LOWER CAPE AND
OTHER ISLANDS WILL RECEIVE WARNING LEVEL SNOWFALL THOUGH NOT QUITE
AS MUCH AS INLAND AREAS. AS OUR FIRST THOUGHTS...WE THINK THAT ABOUT
8 TO 14 INCHES OF SNOW WILL FALL...WITH LOWER AMOUNTS ON THE OUTER
CAPE AND NANTUCKET. THIS CAN AND WILL LIKELY CHANGE AS WE GET CLOSER
TO THE EVENT.

THE NEXT PROBLEM TO LOOK AT IS THE WIND. WILL SEE NE WINDS
INCREASING OVERNIGHT...WITH GUSTS UP TO 30-35 MPH. GUSTS COULD
APPROACH 40 MPH ALONG THE IMMEDIATE COAST...AND EVEN HIGHER GUSTS
POSSIBLE AGAIN ON THE OUTER CAPE AND NANTUCKET. SO...THE NEXT
QUESTION IS...WILL WE SEE BLIZZARD CONDITIONS.  AT THIS POINT...
FEEL THE CHANCE IS LOW...BUT MAY SEE NEAR BLIZZARD CONDITIONS FOR A
TIME /VSBY BELOW 1/4 MILE AND WINDS SUSTAINED OR FREQUENT GUSTS OF
35 MPH OR GREATER FOR AT LEAST 3 CONSECUTIVE HOURS/.

EXPECT THE HEAVIEST SNOW TO FALL LATE TUESDAY NIGHT THROUGH MIDDAY
WEDNESDAY...THEN LIGHTER SNOW WILL LINGER ACROSS CENTRAL AND EASTERN
AREAS THROUGH THE DAY. ACROSS THE CT VALLEY...SNOW SHOULD START
TAPERING OFF DURING THE AFTERNOON. MAY STILL SEE SNOW LINGERING
ALONG THE COAST INTO WEDNESDAY NIGHT...BUT AS THE STORM MOVES S OF
NOVA SCOTIA...STEADY PRECIP SHOULD FINALLY SHUT OFF BY LATE EVENING.
WILL STILL SEE BLUSTERY NW WINDS WHICH WILL BLOW THE NEWLY FALLEN
SNOW AROUND. ALSO...MAY SEE OCEAN EFFECT SNOW SHOWERS FLIRTING WITH
THE OUTER CAPE THROUGH THE NIGHT THOUGH SHOULD REMAIN E OF THAT
AREA.

OVERALL...EXPECT A BIG HIT WITH THIS STORM FOR ABOUT AN 18-24 HOUR
DURATION. MAIN EFFECT WILL BE ALL THE SNOW THAT WILL DUMP ON THE
REGION...THEN WILL BLOW AROUND WITH N-NW WINDS MAINLY DURING
WEDNESDAY.

41
In this thread:
significant/very significant Snowstorm/Blizzard for Northeast Tue/Wed?? - Fred, 1/8/2011, 5:19 pm
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