MESOSCALE DISCUSSION 0513
   NWS STORM PREDICTION CENTER NORMAN OK
   1126 AM CDT SAT APR 18 2009
   
   AREAS AFFECTED...PORTIONS E-CENTRAL/SE TX.
   
   CONCERNING...TORNADO WATCH 165...
   
   VALID 181626Z - 181830Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 165 CONTINUES.
   
   CONTINUE WW.  AREAS FARTHER E TO NEAR LA BORDER -- WHERE AIR MASS
   HAS MOISTENED DURING PAST FEW HOURS -- WILL BE MONITORED FOR
   POSSIBILITY OF ADDITIONAL WW.
   
   BROAD AREA OF PRECIP AND EMBEDDED TSTMS WILL MOVE SLOWLY EWD ACROSS
   THIS REGION...SUPPORTED IN PART BY SLOW DIURNAL DESTABILIZATION AND
   LOW LEVEL MOISTURE ADVECTION/TRANSPORT.  CORRIDOR OF ENHANCED SFC
   VORTICITY ALSO IS EVIDENT WITHIN THIS CONVECTIVE PLUME...ALONG AND
   JUST W OF VCT-OCH LINE.  0-1 KM SRH OF 200-35 J/KG IS EVIDENT ALONG
   WITH FAVORABLE STORM-RELATIVE INFLOW INVOF BROAD/40-50 KT SLY LLJ
   OVER AND E OF SFC VORTICITY RIBBON.  AS SOME CELLS MOVE THROUGH THAT
   CORRIDOR...RAPID SUPERCELL DEVELOPMENT WITH SMALL BUT TIGHT MESO
   CIRCULATIONS TAKES PLACE.
   
   ALONG SRN EDGE OF PRECIP AREA...GRADUAL DIURNAL HEATING WILL
   CONTINUE IN NEAR-SFC INFLOW LAYER...BOOSTING MLCAPE INTO 1000-2000
   J/KG...WITH LITTLE OR NO CINH EVIDENT IN MODIFIED RUC SOUNDINGS. 
   POTENTIAL FOR ADDITIONAL SUPERCELLS MAY BE MAXIMIZED CLOSE TO SRN
   PERIPHERY OF MCS WHERE GREATER INSTABILITY IS LIKELY.  FARTHER
   N...INSTABILITY APPEARS MORE MRGL AND SPOTTY...BUT APPARENTLY
   SUFFICIENT TO SUPPORT AT LEAST BRIEF/SFC-BASED INTENSIFICATION OF
   EMBEDDED TSTMS THAT OCCURRED FROM 13-15Z...RESULTING IN AT LEAST ONE
   TORNADO REPORT IN ROBERTSON COUNTY WITH STORM THAT SINCE HAS
   WEAKENED OVER LEON COUNTY.
   
   ADDITIONAL TSTMS...WHICH APPEAR ELEVATED ABOVE RELATIVELY STABLE
   SFC-BASED LAYER BASED ON MODIFIED RAOBS AND RUC SOUNDINGS...HAVE
   FORMED N OF WW OVER ACT/TPL AREAS. THIS ACTIVITY MAY STRUGGLE TO
   MAINTAIN INTENSITY WHILE MOVING INTO AIR MASS AFFECTED BY EARLIER
   CONVECTION...BUT ALSO WILL MOVE INTO STRONGER SHEAR ENVIRONMENT OF
   NRN PORTIONS WW.
   
   ..EDWARDS.. 04/18/2009
   
   
   ATTN...WFO...LCH...SHV...HGX...FWD...CRP...EWX...
   
   LAT...LON   28399632 29089684 29359658 29599679 29969654 30489686
               31039621 31759649 32149501 31839499 31779403 31089372
               30709396 30239377 29939401 29589431 28399632