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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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