MESOSCALE DISCUSSION 0023
   NWS STORM PREDICTION CENTER NORMAN OK
   0740 PM CST SAT JAN 17 2004
   
   AREAS AFFECTED...FAR SERN PA/SRN NJ...NRN DE/MD...DC AND NERN VA
   
   CONCERNING...WINTER MIXED PRECIPITATION 
   
   VALID 180140Z - 180745Z
   
   A MIX OF SLEET AND SNOW WILL CHANGE TO FREEZING RAIN/SLEET OVER NRN
   MD AND FAR SERN PA/NRN DE IN THE NEXT 3 HOURS. FARTHER SOUTH OVER
   SRN MD AND NERN VA...LIGHT SLEET WILL CHANGE OVER TO FREEZING RAIN
   WITH THE ONSET OF HEAVIER PRECIPITATION AFTER 18/04Z. HOURLY LIQUID
   EQUIVALENT PRECIPITATION RATES FROM 0.05 TO 0.10 INCHES WILL BE
   POSSIBLE BETWEEN 18/04 AND 18/08Z WITH TOTAL ACCUMULATIONS IN SOME
   AREAS EXCEEDING 0.25 INCH.
   
   IR SATELLITE/RADAR IMAGERY AND VWP DATA CONFIRM AN INTENSIFYING LOW
   LEVEL JET OVER KY/TN...AS NOTED BY COOLING CLOUD TOPS OVER KY AND
   INTENSIFYING RADAR ECHOS. MID LEVEL WARM CONVEYOR PRECIP BAND HAS
   BEEN EFFICIENT OVER THE LAST SEVERAL HOURS IN SATURATING THE 850-700
   MB LAYER AS EVIDENT ON THE 00Z DULLES SOUNDING. IN THIS AREA LIGHT
   PRECIPITATION HAS DEVELOPED. 
   
   LOW LEVELS FARTHER S OVER SRN MD AND CENTRAL VA REMAIN DRY AS NOTED
   ON THE 00Z BLACKSBURG SOUNDING.  DESPITE THIS...A COMBINATION OF
   SEVERAL FACTORS MAY LEAD TO A MODERATE ICING/SLEET EVENT BEGINNING
   AROUND 18/04Z. TEMPERATURES SHOULD REMAIN AOB FREEZING NORTH OF A
   LINE FROM ROUGHLY LYNCHBURG TO RICHMOND...BECAUSE OF
   EVAPORATIVE/WET-BULB EFFECTS.  DRIER LOW LEVEL SELYS OVER ERN NC
   SHOULD ALLOW FOR LITTLE MOVEMENT OF THE SFC FREEZING LINE THROUGH
   MOST OF THE EVENT. COUPLED UPPER JET STRUCTURE WILL CONTINUE TO
   DEVELOP BETWEEN WRN LAKES UPPER TROUGH AND GULF COAST UPPER TROUGH
   AND AID IN A DEEP COLUMN OF VERTICAL MOTION CENTERED OVER THE
   AREA...IN ADDITION TO A STRENGTHENING LOW LEVEL WARM/MOISTURE
   ADVECTION. THE LOW LEVEL JET SHOULD AID IN SHIFTING THE ELEVATED
   WARM LAYER...NOTED ON REGIONAL SOUNDINGS FARTHER SOUTH/WEST...INTO
   SERN PA/NRN MD/DE THROUGH 18/06Z. THIS WILL ALLOW FOR A CHANGE OF
   SLEET/SNOW TO SLEET/FREEZING RAIN MIX IN THIS AREA.  FARTHER SOUTH
   OVER SRN MD/NERN VA AND THE DC METRO AREA...INITIAL SLEET SHOULD
   CHANGE OVER TO FREEZING RAIN SHORTLY AFTER 18/03Z DUE TO THE
   PRESENCE OF A DEEPER/LOWER ELEVATED WARM LAYER.
   
   ..CROSBIE.. 01/18/2004
   
   
   ATTN...WFO...PHI...AKQ...CTP...LWX...
   
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