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Mesoscale Discussion 8
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   MESOSCALE DISCUSSION 0008
   NWS STORM PREDICTION CENTER NORMAN OK
   0859 AM CST SAT JAN 03 2015

   AREAS AFFECTED...MUCH OF PA AND WRN NY

   CONCERNING...WINTER MIXED PRECIPITATION 

   VALID 031459Z - 031900Z

   SUMMARY...PTYPE TRANSITION FROM SNOW/SLEET TO FREEZING RAIN/RAIN
   WILL OCCUR WITHIN A SWATH OF WIDESPREAD LIGHT TO LOCALLY MODERATE
   PRECIPITATION. ICE ACCRETION RATES OF .03-.06 IN/HR ARE
   LIKELY...WITH THE GREATEST LONGEVITY OF FREEZING RAIN EXPECTED FROM
   PARTS OF CNTRL PA TO SWRN NY.

   DISCUSSION...TIME-SERIES OF REGIONAL VWP DATA DEPICT STRENGTHENING
   LOW-LEVEL S/SWLYS WITH ENLARGED CYCLONIC HODOGRAPHS INDICATIVE OF
   ROBUST WAA/ISENTROPIC ASCENT. BROAD SWATH OF MIXED PRECIPITATION
   SHOULD CONTINUE TO PROGRESS/EXPAND NEWD ACROSS THE NRN APPALACHIANS
   INTO EARLY AFTERNOON. 12Z PIT/IAD RAOBS SAMPLED AN ABOVE-FREEZING
   WARM NOSE SATURATED TO 3-4 DEG C BETWEEN 850-800 MB. FORECAST
   SOUNDINGS AND RAP/NAM/SREF PTYPE GUIDANCE ALL SUGGEST THAT PTYPE
   WILL BE TRANSITORY WITHIN SUCH A STRONG WAA REGIME. GIVEN OBSERVED
   SURFACE TEMPERATURES FROM 25-30 DEG F...INITIAL LIGHT SLEET/SNOW
   SHOULD CHANGE OVER TO PREDOMINANT FREEZING RAIN BEFORE BECOMING RAIN
   AS TEMPERATURES DIABATICALLY WARM AOA 32 DEG F. MULTIPLE HOURS OF
   ICE ACCRETION APPEARS MOST PROBABLE FROM CNTRL PA TO SWRN NY INTO
   EARLY AFTERNOON.

   ..GRAMS.. 01/03/2015


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

   LAT...LON   41667973 42297957 42837841 42807691 42617591 42277531
               41637517 41047553 40367661 40037740 39877785 39917838
               40127885 40717904 41667973 

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Page last modified: January 03, 2015
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