SWOMCD
SPC MCD 110504
NYZ000-NJZ000-PAZ000-110800-
MESOSCALE DISCUSSION 2441
NWS STORM PREDICTION CENTER NORMAN OK
1104 PM CST WED DEC 10 2008
AREAS AFFECTED...PORTIONS OF PA...SERN NY...NRN NJ
CONCERNING...FREEZING RAIN
VALID 110504Z - 110800Z
FREEZING RAIN ALREADY BEING OBSERVED ACROSS A FEW PA SITES WILL VERY
GRADUALLY INCREASE IN COVERAGE OVER THE NEXT 6 HOURS...WITH GREATER
INCREASES TOWARDS THE 10 TO 12Z TIME FRAME. AROUND 10 TO 12Z AND
AFTER...RATES WILL INCREASE AS WELL...WITH MORE SIGNIFICANT
ACCUMULATIONS EXPECTED AFTER 12Z.
A SURFACE COLD FRONT HAS PUSHED SEWD...AND NOW EXTENDS ALONG THE NEW
ENGLAND COAST SWWD INTO CNTRL VA AND ALONG THE APPALACHIANS. WEAK
COLD ADVECTION IS OCCURRING AT THE SURFACE BEHIND THIS...WITH
NIGHTTIME COOLING CONTRIBUTING AS WELL. 00Z KPIT SOUNDING SHOWS A
SATURATED COLUMN BELOW 650 MB...WITH DRYING ABOVE CURRENTLY
INHIBITING GREATER FREEZING RAINFALL RATES. HOWEVER...AN UPPER LOW
IN THE WRN GULF WILL CONTINUE TO ALLOW DEEP SLY/SWLY WINDS TO ADVECT
MOISTURE NWD/NEWD...AND THIS WILL GRADUALLY ALLOW FOR SATURATION TO
OCCUR...BECOMING NEARLY OR COMPLETELY SATURATED BY 12Z. AS THE UPPER
LOW MOVES ENEWD...A LOW LEVEL BAROCLINIC ZONE WILL BEGIN TO TIGHTEN
FROM SWRN PA THROUGH NJ/SERN NY AND PORTIONS OF THE NEW ENGLAND
COAST. ALTHOUGH CURRENT MODEL QPF SHOW HIGHER PRECIPITATION RATES
SOUTH OF THIS BOUNDARY...WARM ADVECTION AND OVERRIDING PRECIPITATION
SHOULD ALLOW FOR A BAND OF FREEZING RAIN TO SET UP JUST NORTH OF IT.
SURFACE TEMPERATURES IN THESE AREAS ARE EXPECTED TO REMAIN
SUBFREEZING EVEN AFTER DAYBREAK. ADDITIONALLY...UPPER DIVERGENCE
WILL INCREASE THROUGH THE MORNING AHEAD OF THE APPROACHING UPPER
LOW...CONTRIBUTING TO INCREASING VERTICAL MOTION AND GREATER
FREEZING RAINFALL RATES BY EARLY MORNING.
..HURLBUT.. 12/11/2008
...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...OKX...ALY...PHI...BGM...CTP...PBZ...
LAT...LON 40917550 40697761 39958003 40458041 41098013 41587741
41937545 41957443 41397425 41047475 40917550
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