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Mesoscale Discussion 114
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   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


   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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