MESOSCALE DISCUSSION 1804
   NWS STORM PREDICTION CENTER NORMAN OK
   0558 PM CDT THU OCT 20 2016

   AREAS AFFECTED...PORTIONS OF WRN/CNTRL PA...NRN WV...AND FAR WRN MD

   CONCERNING...SEVERE THUNDERSTORM WATCH 499...

   VALID 202258Z - 210030Z

   THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 499
   CONTINUES.

   SUMMARY...A RISK FOR LARGE HAIL...DAMAGING WINDS...AND PERHAPS A
   BRIEF TORNADO WILL CONTINUE ACROSS PARTS OF WW 499 FOR THE NEXT
   SEVERAL HOURS BEFORE DIMINISHING.

   DISCUSSION...RECENT RADAR TRENDS SHOW SEVERAL DISCRETE CELLS
   OCCASIONALLY EXHIBITING SUPERCELL CHARACTERISTICS ACROSS WRN PA THAT
   ARE LOCATED ALONG A COLD FRONT. AS THESE THUNDERSTORMS MOVE
   EWD/NEWD...THEY WILL ENCOUNTER A WEAKLY UNSTABLE AIRMASS
   CHARACTERIZED BY MLCAPE OF 500-1000 J/KG. SELY SFC WINDS VEER WITH
   HEIGHT TO SWLY WHILE ALSO STRENGTHENING. EFFECTIVE BULK SHEAR VALUES
   OF 40-50 KT REMAIN SUPPORTIVE OF DISCRETE STORM MODES...WITH LARGE
   HAIL AND DAMAGING WINDS THE MAIN THREATS. AN ISOLATED TORNADO MAY
   ALSO BE POSSIBLE WITH EFFECTIVE SRH RANGING GENERALLY FROM 150-250
   M2/S2 INTO CNTRL PA. THE OVERALL SEVERE THREAT SHOULD BEGIN TO
   LESSEN WITH THE LOSS OF DAYTIME HEATING OVER THE NEXT FEW HOURS.

   ..GLEASON.. 10/20/2016


   ATTN...WFO...CTP...PBZ...

   LAT...LON   40027969 41617864 41647760 41187708 40067784 39747896
               39257942 39588005 40027969