ZCZC SPCSWOMCD ALL ACUS11 KWNS 181857 SPC MCD 181857 TXZ000-182100- MESOSCALE DISCUSSION 0237 NWS STORM PREDICTION CENTER NORMAN OK 0157 PM CDT FRI MAR 18 2016 AREAS AFFECTED...THE TEXAS EDWARDS PLATEAU/HILL COUNTRY AND ADJACENT RIO GRANDE VALLEY CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE VALID 181857Z - 182100Z PROBABILITY OF WATCH ISSUANCE...60 PERCENT SUMMARY...SCATTERED STRONG TO SEVERE STORM DEVELOPMENT APPEARS POSSIBLE ACROSS THE REGION THROUGH THE 20-00Z TIME FRAME. STRONGEST ACTIVITY LIKELY WILL BE CAPABLE OF PRODUCING LARGE HAIL AND LOCALLY STRONG WIND GUSTS. A WATCH MAY BE NEEDED AS EARLY AS THE NEXT HOUR OR TWO. DISCUSSION...LIGHT SOUTHEASTERLY SURFACE FLOW UP THE RIO GRANDE VALLEY...AND INTO THE EDWARDS PLATEAU/HILL COUNTRY...AS WELL AS HIGHER TERRAIN WEST OF THE RIO GRANDE RIVER...IS MAINTAINING HIGH BOUNDARY LAYER MOISTURE CONTENT IN ADVANCE OF A SOUTHWARD ADVANCING COLD FRONT. AND INSOLATION BENEATH WARM/CAPPING ELEVATED MIXED LAYER AIR IS CONTRIBUTING TO THE DEVELOPMENT OF MODERATE TO STRONG POTENTIAL INSTABILITY. THUNDERSTORMS HAVE ALREADY INITIATED OFF THE MOUNTAINS WEST OF THE RIVER /ABOUT 75 MI WSW OF DEL RIO/...BUT INHIBITION OTHERWISE REMAINS STRONG FOR BOUNDARY LAYER BASED DEVELOPMENT. GIVEN THE GENERALLY LIGHT NATURE OF THE DEEP LAYER WESTERLY MEAN FLOW...IT MAY TAKE SOME TIME FOR CONVECTION WEST OF THE RIVER TO PROPAGATE OFF THE HIGHER TERRAIN AND CROSS THE RIVER INTO SOUTH TEXAS. GUIDANCE IS SUGGESTIVE THAT THIS MAY NOT BE UNTIL EARLY EVENING. HOWEVER...THE HIGH RESOLUTION RAPID REFRESH...AMONG OTHER MODEL OUTPUT...HAS BEEN SUGGESTIVE THAT THE STORM INITIATION COULD OCCUR ACROSS THE EDWARDS PLATEAU/HILL COUNTRY AS EARLY AS 20-21Z. IT APPEARS AT LEAST POSSIBLE THAT FORCING ASSOCIATED WITH SOUTHWARD PROPAGATING GRAVITY WAVES EVIDENT IN SATELLITE IMAGERY COULD CONTRIBUTE TO SUFFICIENT WEAKENING OF INHIBITION TO ALLOW STORMS TO DEVELOP. IF THIS OCCURS...THE THERMODYNAMIC ENVIRONMENT APPEARS MORE THAN SUPPORTIVE OF SEVERE STORMS CAPABLE OF PRODUCING LARGE HAIL...AND AT LEAST LOCALLY STRONG WIND GUSTS LATE THIS AFTERNOON. ..KERR/WEISS.. 03/18/2016 ...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT... ATTN...WFO...CRP...EWX...SJT...MAF... LAT...LON 29570222 30220226 30880179 30439977 30539894 29889825 29249888 28760004 28109986 27099959 27099959 27620159 29570222 NNNN