MESOSCALE DISCUSSION 0119
   NWS STORM PREDICTION CENTER NORMAN OK
   0533 PM CST MON FEB 21 2011
   
   AREAS AFFECTED...PORTIONS CENTRAL/SERN OH...NRN WV...EXTREME SWRN
   PA...NRN VA...NWRN THROUGH CENTRAL MD INCLUDING PANHANDLE...DC.
   
   CONCERNING...WINTER MIXED PRECIPITATION 
   
   VALID 212333Z - 220430Z
   
   EXISTING FREEZING RAIN SITUATION OVER PORTIONS CENTRAL/SRN OH AND
   NRN PANHANDLE OF WV SHOULD SHIFT SLIGHTLY SWD.  OVER CENTRAL-ERN
   PARTS OF THIS CORRIDOR...FROM NERN WV ACROSS NRN MD...CURRENT AREAS
   OF FREEZING RAIN ARE EXPECTED TO TRANSITION TO SNOW FROM N-S WITH
   TIME...ALONG SRN LIMB OF REGIME COVERED IN SPC MESOSCALE DISCUSSION
   118.  MEANWHILE...HEAVIER PRECIP IS FCST TO SPREAD ACROSS THIS
   REGION FROM WNW-ESE...AS RAIN CHANGES TO FREEZING RAIN...WITH RATES
   .05-.1 INCH/HOUR...LOCALLY/BRIEFLY HEAVIER IN CORES.
   
   23Z SFC MESOANALYSIS SHOWS WAVY FREEZING LINE FROM CENTRAL OH NEAR
   CMH EWD NEAR HLG...ESEWD NEAR CBE...MRB...FDK...THEN NEWD PAST TO
   RDG.  THIS FREEZING LINE WILL SHIFT SWD THROUGH REMAINDER EVENING
   PRIMARILY BECAUSE OF...
   1. BOUNDARY LAYER CAA...AS SFC PRESSURE RISES NOW ANALYZED OVER
   MID-ATLANTIC REGION REINFORCE LOWER-THETAE AIR MASS N OF FRONTAL
   ZONE
   2. SUBTLE DIABATIC SFC COOLING...AND ESPECIALLY
   3. EVAPORATIVE/WET-BULB EFFECTS FROM PRECIP FALLING INTO LAYER OF
   DRY ADVECTION N OF FRONT.
   
   THESE FACTORS WILL FOSTER CHANGE FROM RAIN TO FREEZING RAIN IN AREAS
   NOW S OF THAT LINE.  MEANWHILE...TIME SERIES OF MODIFIED RUC
   SOUNDINGS SUGGESTS SUPERFREEZING LAYER ABOVE SFC WILL COOL ON N SIDE
   OF THIS CORRIDOR...LEADING TO PHASE TRANSITION FROM LIQUID TO SNOW
   FROM N-S...WHILE STILL REMAINING WARM ENOUGH TO SUPPORT LIQUID
   ELSEWHERE.  MOISTURE TRANSPORT INTO THIS REGION SHOULD CONTINUE ON
   NOSE OF LONG-FETCH/40-45 KT SWLY LLJ...WHILE SUPPORTIVE
   ISENTROPIC/FRONTOGENETIC ASCENT MAXIMA SHIFT EWD ALONG THIS
   CORRIDOR.  STRONGEST FRONTOGENETIC FORCING SHOULD BE IN 750-850 MB
   COLUMN...FROM WITHIN TO JUST BELOW BASE OF ELEVATED WARM LAYER...AND
   NE OF EWD-MOVING SFC LOW.  ON ERN END OF DISCUSSION AREA...OVER
   NRN/CENTRAL MD...COOLING FROM 850 MB TO SFC MAY SHRINK WARM-LAYER
   DEPTH ALOFT AND SUPPORT OCNL SLEET...HOWEVER...PRIND FREEZING RAIN
   WILL BE PRIMARY PHASE OVER MOST OF THIS SWATH BEFORE CHANGE TO SNOW.
   
   ..EDWARDS.. 02/21/2011
   
   
   ATTN...WFO...CTP...LWX...PBZ...RLX...ILN...
   
   LAT...LON   40148317 40158252 40178069 39907941 39657770 39377656
               38987644 38787666 38827752 39157894 39408053 39448166
               39498294 39668354 40108335 40148317