MESO: Mesoscale Discussion 2278

ACUS11 KWNS 291701
SWOMCD
SPC MCD 291701
MAZ000-NHZ000-CTZ000-VTZ000-NYZ000-NJZ000-PAZ000-292200-

MESOSCALE DISCUSSION 2278
NWS STORM PREDICTION CENTER NORMAN OK
1201 PM CDT SAT OCT 29 2011

AREAS AFFECTED...CNTRL AND ERN PA...NRN NJ...SERN NY...NRN CT...NRN
RI...WRN AND CNTRL MA...SRN VT AND NH

CONCERNING...HEAVY SNOW

VALID 291701Z - 292200Z

BANDS OF MODERATE TO HEAVY SNOW WILL SHIFT ENEWD THROUGH PA...SERN
NY AND SRN NEW ENGLAND DURING THE AFTERNOON. SNOWFALL RATES OF 1+
INCH PER HOUR WILL REMAIN LIKELY IN THE HEAVIEST BANDS AND MIGHT
OCCASIONALLY APPROACH 2 INCHES PER HOUR.

EARLY THIS AFTERNOON...MODERATE TO HEAVY SNOW BAND HAS SET UP FROM
CNTRL AND ERN PA ENEWD THROUGH NRN NJ AND SERN NY. SURFACE
TEMPERATURES IN THIS REGION ARE AT OR A FEW DEGREES ABOVE FREEZING
WITH WET BULB TEMPERATURES AROUND 32F. THE 12Z RAOBS AND RUC PFCS
INDICATE SUB-FREEZING WET BULB TEMPERATURES JUST ABOVE THE SURFACE
THROUGH THE REMAINDER OF THE TROPOSPHERE INLAND FROM THE COAST.
HOWEVER...THE SURFACE WARM LAYER WILL LIKELY REMAIN DEEP ENOUGH TO
KEEP THE PRECIPITATION RAIN IN MOST AREAS WITHIN ABOUT 30 SM OF THE
COAST.

THE SNOW IS DEVELOPING WITHIN A DEEP BAROCLINIC/FRONTOGENETIC ZONE
THAT EXTENDS FROM THE MID ATLANTIC REGION NEWD THROUGH SRN NEW
ENGLAND. WV IMAGERY SHOWS AN EXPANDING BAROCLINIC LEAF AND COOLING
CLOUD TOPS OVER THE NERN STATES JUST DOWNSTREAM FROM A NEGATIVELY
TILTED SHORTWAVE TROUGH AND ITS ASSOCIATED MID-LEVEL JET PIVOTING
NEWD THROUGH THE MID ATLANTIC REGION. SURFACE LOW OFF THE MID
ATLANTIC COAST WILL DEEPEN AND LIFT NWD TOWARD SRN NEW ENGLAND IN
ASSOCIATION WITH UPPER DIVERGENCE ACCOMPANYING THE UPPER JET. IN THE
PROCESS...FRONTOGENETIC FORCING AND ISENTROPIC ASCENT SHOULD
INCREASE FROM ERN PA THROUGH SRN NEW ENGLAND DURING THE AFTERNOON.
THIS ZONE OF ASCENT IS OCCURRING WITHIN THE PORTION OF THERMODYNAMIC
PROFILE FAVORABLE FOR SNOW GROWTH. IN ADDITION...PFCS AND CROSS
SECTION DATA INDICATE PRESENCE OF AT LEAST WEAK UPRIGHT AND
SLANTWISE INSTABILITY SUGGESTING CONVECTIVE ENHANCEMENT ALSO REMAINS
LIKELY. WET BULB TEMPERATURES IN THE NEAR SURFACE LAYER WILL REMAIN
AT OR ABOVE FREEZING...PROMOTING A WETTER SNOW...AND THIS COULD
REDUCE ACCUMULATION RATES SOMEWHAT DESPITE THE PRESENCE OF LARGE
FLAKES.

..DIAL.. 10/29/2011

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...GYX...BOX...OKX...ALY...PHI...BGM...CTP...

LAT...LON 42107162 41477315 40867422 40127569 40237758 41237755
42527515 43187213 42827118 42107162

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