MESO: Mesoscale Discussion 0114

ACUS11 KWNS 191058
SWOMCD
SPC MCD 191057
NYZ000-PAZ000-MDZ000-191400-

MESOSCALE DISCUSSION 0114
NWS STORM PREDICTION CENTER NORMAN OK
0457 AM CST WED FEB 19 2014

AREAS AFFECTED...PARTS OF NRN MARYLAND THRU MUCH OF CNTRL/ERN
PENNSYLVANIA AND ADJACENT SRN NEW YORK STATE

CONCERNING...FREEZING RAIN

VALID 191057Z - 191400Z

SUMMARY...A QUICK GLAZING OF MOST UNTREATED ROAD SURFACES AND
WALKWAYS APPEARS POSSIBLE DURING THE 12-15Z TIME FRAME...ASSOCIATED
WITH LIGHT TO OCCASIONALLY MODERATE FREEZING RAIN.

DISCUSSION...MODEL FORECAST SOUNDINGS INDICATE THAT INITIALLY DRY
LOWER/MID TROPOSPHERIC THERMODYNAMIC PROFILES ALONG AND EAST OF THE
ALLEGHENY MOUNTAINS INTO EASTERN PORTIONS OF THE ALLEGHENY PLATEAU
WILL QUICKLY SATURATE DURING THE NEXT FEW HOURS. THIS IS EXPECTED
TO OCCUR IN RESPONSE TO EVAPORATION OF PRECIPITATION FROM
ALOFT...AND RAPID MOISTURE ADVECTION ON DEEP LAYER SOUTHERLY
FLOW...AHEAD OF A SIGNIFICANT SHORT WAVE TROUGH NOW TURNING EASTWARD
INTO THE UPPER OHIO VALLEY.

ALTHOUGH THIS LIKELY WILL REDUCE THE DEPTH OF THE WARM LAYER ABOVE
THE LINGERING SHALLOW SUB-FREEZING BOUNDARY LAYER ALONG TO THE EAST
OF THE HIGHER TERRAIN...IT APPEARS THAT ENOUGH OF AN ELEVATED WARM
LAYER WILL PERSIST...AS LOW-LEVEL WARM ADVECTION CONTINUES...TO
SUPPORT MOSTLY FREEZING RAIN. GUIDANCE INDICATES AN AREA OF STRONG
UPWARD VERTICAL MOTION...SUPPORTED BY FORCING ASSOCIATED WITH
APPROACHING IMPULSE...WILL OVERSPREAD MUCH OF THE REGION DURING THE
12-15Z TIME...MAINTAINING LIGHT TO OCCASIONALLY MODERATE
PRECIPITATION RATES THAT COULD YIELD RAIN TOTALS UP TO NEAR 1/4
INCH.

GIVEN THE INITIALLY COLD GROUND CONDITIONS...EVEN LIGHTER AMOUNTS
PROBABLY WILL LEAD TO A QUICK GLAZING OF MOST UNTREATED ROAD
SURFACES AND WALKWAYS...PARTICULARLY NEAR THE AXIS OF COLDEST
SURFACE TEMPERATURES SOUTH AND EAST OF STATE COLLEGE PA INTO THE
WILLIAMSPORT PA...ELMIRA AND BINGHAMTON NY AREAS. FARTHER TO THE
SOUTH AND EAST...NEAR THE EASTERN PENNSYLVANIA/MARYLAND BORDER...
AND NORTHWARD THROUGH THE DELAWARE VALLEY...THE BOUNDARY LAYER MAY
WARM ABOVE FREEZING PRIOR TO THE ONSET OF PRECIPITATION LATER THIS
MORNING.

..KERR.. 02/19/2014

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

ATTN...WFO...ALY...PHI...BGM...CTP...LWX...

LAT...LON 40677831 41627709 42177641 42587562 42497462 41527509
40777522 40057568 39667658 39827763 40127838 40677831

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