MESO: Mesoscale Discussion 2247

ACUS11 KWNS 131016
SWOMCD
SPC MCD 131016
NYZ000-PAZ000-WVZ000-OHZ000-131415-

MESOSCALE DISCUSSION 2247
NWS STORM PREDICTION CENTER NORMAN OK
0416 AM CST SUN DEC 13 2009

AREAS AFFECTED...PARTS OF ERN OH/WRN-CENTRAL PA/SWRN AND SOUTH
CENTRAL NY

CONCERNING...FREEZING RAIN

VALID 131016Z - 131415Z

A BRIEF PERIOD OF FREEZING RAIN IS EXPECTED TO DEVELOP OVER ERN
OH/WRN PA BETWEEN 11-13Z...BEFORE TRANSITIONING TO A SNOW/RAIN
MIXTURE...THEN RAIN BY MID-LATE MORNING. FREEZING RAIN RATES COULD
RANGE FROM 0.1-0.2 IN/HR. MEANWHILE...A MORE PROLONGED PERIOD OF
FREEZING RAIN RATES /0.1-0.2 IN/HR/ IS EXPECTED ACROSS PARTS OF
CENTRAL PA INTO SOUTH CENTRAL NY...WITH THIS ACTIVITY DEVELOPING
BETWEEN 12-16Z AND CONTINUING THROUGH 18Z.

MID LEVEL SHORTWAVE TROUGH...CURRENTLY TRACKING ENEWD ACROSS THE MID
MS VALLEY PER WATER VAPOR IMAGERY...WILL AMPLIFY SOME AS IT MOVES
THROUGH THE OH VALLEY REACHING PA/NY BY 14/00Z. DIFFLUENT MID-UPPER
LEVEL FLOW AHEAD OF THIS TROUGH COUPLED WITH INCREASING LOW LEVEL
WAA ATTENDANT TO A STRENGTHENING SWLY LLJ /50-60 KT/ FROM WV TO NY
WILL PROVIDE AMPLE DEEP LAYER ASCENT TO MAINTAIN SWATH OF
PRECIPITATION SPREADING TOWARD THIS REGION FROM THE LOWER-MID OH
VALLEY.

...PARTS OF ERN OH/WRN PA/FAR SWRN NY...
CURRENT OBSERVATIONS SHOW SURFACE TEMPERATURES RISING INTO THE LOWER
30S OVER ERN OH INTO PARTS OF FAR WRN PA. HOWEVER...A PRE-EXISTING
DRY BOUNDARY LAYER WITH SURFACE WET BULB TEMPERATURES IN THE MID 20S
SUGGESTS PRECIPITATION SHOULD OCCUR AS FREEZING RAIN FOR A BRIEF
/1-2 HOUR PERIOD/. EVENTUALLY... STRONG LOW LEVEL WAA WILL BECOME
SUFFICIENT TO MODIFY THE BOUNDARY LAYER WITH PRECIPITATION
TRANSITIONING TO SNOW/RAIN AND THEN RAIN AS SURFACE TEMPERATURES
RISE ABOVE 32 F.

...CENTRAL PA AND SOUTH CENTRAL NY...
CURRENT OBSERVATIONS SHOW SUB-FREEZING SURFACE TEMPERATURES
/LOWER-MID 20S/ FROM CENTRAL PA INTO SOUTH CENTRAL NY. AS THE
PRECIPITATION SPREADS FARTHER DOWNSTREAM INTO THIS REGION WITH THE
APPROACH OF THE MID LEVEL TROUGH...EVAPORATIVE COOLING SHOULD
MAINTAIN THE SUB-FREEZING TEMPERATURES...WHILE INCREASING WAA ABOVE
THE COLDER BOUNDARY LAYER WILL SUPPORT FREEZING RAIN. INCREASING
ASCENT WILL ENHANCE THE PRECIPITATION RATES /0.1-0.2 INCH PER HOUR/
FROM MID MORNING INTO THE EARLY AFTERNOON.

..PETERS.. 12/13/2009

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

...NOTICE...
SPC WINTER WEATHER MESOSCALE DISCUSSIONS WILL BE ISSUED ON A
SCHEDULED BASIS FROM DECEMBER 1 THROUGH FEBRUARY 28...FOUR
TIMES A DAY...AROUND 00 UTC...06 UTC...12 UTC...AND 18 UTC
FOR SIGNIFICANT SHORT RANGE WINTER WEATHER EVENTS.

ATTN...WFO...BGM...BUF...CTP...PBZ...CLE...

LAT...LON 42837597 42137573 40627722 40507767 40177803 40207889
40517916 40477989 40368043 40288106 41308106 41518070
41738027 42197945 42397893 42557816 42837597

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