MESOSCALE DISCUSSION 0642
   NWS STORM PREDICTION CENTER NORMAN OK
   0755 PM CDT TUE MAY 14 2013
   
   AREAS AFFECTED...SRN PART OF THE EDWARDS PLATEAU INTO PORTIONS OF
   SOUTH AND SOUTH CENTRAL TX
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 150055Z - 150300Z
   
   PROBABILITY OF WATCH ISSUANCE...40 PERCENT
   
   SUMMARY...ONGOING TSTMS LOCATED OVER NRN CHIHUAHUA TO ALONG AND JUST
   N OF THE INTERNATIONAL BORDER IN SRN BREWSTER/ADJACENT TERRELL
   COUNTIES ARE EXPECTED TO SPREAD ENEWD THIS EVENING...AFFECTING THE
   SRN PART OF THE EDWARDS PLATEAU AND PORTIONS OF SOUTH AND SOUTH
   CENTRAL TX.  SOME OF THIS ACTIVITY SHOULD BE OR BECOME CAPABLE OF
   PRODUCING SEVERE HAIL AND DAMAGING WIND GUSTS.  THIS POTENTIAL
   SEVERE WEATHER WILL CONTINUE TO BE MONITORED WITH WATCH ISSUANCE
   POSSIBLE YET THIS EVENING.
   
   DISCUSSION...AT 0030Z...REGIONAL RADAR IMAGERY...LIGHTNING DATA AND
   COOLING CLOUD TOPS PER IR IMAGERY SHOWED A CLUSTER OF TSTMS
   EXTENDING FROM NRN CHIHUAHUA MEXICO NWD INTO THE ADJACENT PORTIONS
   OF BREWSTER/TERRELL COUNTIES.  THE DOWNSTREAM ENVIRONMENT ACROSS THE
   EDWARDS PLATEAU INTO THE LOWER RIO GRANDE VALLEY IS MODERATELY
   UNSTABLE GIVEN PRECIPITABLE WATER VALUES EXCEEDING 1-1.5 INCHES AND
   STEEP LAPSE RATES /7.5-8 C/KM AT MIDLEVELS PER 00Z DRT SOUNDING/. 
   DESPITE THE LOSS OF DAY TIME HEATING THROUGH THE
   EVENING...MOISTENING PER A STRENGTHENING SLY LLJ ACROSS THE
   DISCUSSION AREA WILL AID IN DESTABILIZATION BENEATH THE STEEP
   MIDLEVEL LAPSE RATES TO AT LEAST SUSTAIN MODERATE INSTABILITY AFTER
   SUNSET.
   
   MEANWHILE...THE HRRR /INCLUDING RUNS SINCE 21Z/ HAS INDICATED ONE OR
   TWO CLUSTERS OF TSTMS WILL AFFECT THE SRN EDWARDS PLATEAU INTO PARTS
   OF SOUTH AND SOUTH CENTRAL TX THIS EVENING...BUT OVERALL COVERAGE OF
   STRONGER/SEVERE STORMS REMAINS UNCERTAIN.  FORCING FOR ASCENT
   ATTENDANT TO A MIDLEVEL IMPULSE TRACKING NEWD FROM NRN MEXICO INTO
   TX SHOULD SUPPORT THE ONGOING NRN MEXICO TSTM CLUSTER AND NEW TSTM
   ACTIVITY INTO THE DISCUSSION AREA THIS EVENING. 40-50 KT SWLY
   MIDLEVEL WINDS ACCOMPANYING THE IMPULSE AND 30-40 KT SLY LLJ WILL
   RESULT IN STRENGTHENING EFFECTIVE BULK SHEAR FOR STORM ORGANIZATION.
    GIVEN THE ENVIRONMENT ACROSS THE DISCUSSION AREA EXPECTED TO BE
   SUPPORTIVE FOR SEVERE STORMS...REGIONAL RADAR TRENDS WILL BE
   MONITORED AS ONGOING STORMS PROGRESS EWD FROM NRN MEXICO WITH THE
   POTENTIAL FOR WATCH ISSUANCE YET THIS EVENING.
   
   ..PETERS/HART.. 05/15/2013
   
   
   ATTN...WFO...CRP...EWX...SJT...MAF...
   
   LAT...LON   29890178 30430151 30509975 30229902 29539878 28249852
               27579886 27429940 28190026 29220095 29670168 29890178