MESOSCALE DISCUSSION 0170
   NWS STORM PREDICTION CENTER NORMAN OK
   0506 PM CST MON FEB 18 2013
   
   AREAS AFFECTED...ERN TX...WRN LA
   
   CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 
   
   VALID 182306Z - 190030Z
   
   PROBABILITY OF WATCH ISSUANCE...20 PERCENT
   
   SUMMARY...ISOLATED THUNDERSTORM DEVELOPMENT WILL BE POSSIBLE ALONG A
   DRYLINE/PRE-FRONTAL CONFLUENCE ZONE AND SEWD PROGRESSING COLD FRONT
   DURING THE EVENING OVER ERN TX. IF STORMS DEVELOP...THEY ARE
   EXPECTED TO MOVE EWD INTO WRN LA BY 03Z...BEHIND PRE-FRONTAL WARM
   CONVEYOR BELT CONVECTION. MARGINALLY SEVERE HAIL WOULD BE THE
   PRIMARY THREAT...ALONG WITH ISOLATED DAMAGING WIND GUSTS IF ACTIVITY
   CAN ORGANIZE INTO A LINE.
   
   DISCUSSION...MESOANALYSIS AT 22-23Z SHOWS A SURFACE COLD FRONT WAS
   PROGRESSING ESEWD INTO CNTRL AR AND NERN TX. A DRYLINE/PRE-FRONTAL
   CONFLUENCE ZONE EXTENDED SWWD FROM THE NERN TX FRONTAL
   SEGMENT...WHILE WARM CONVEYOR BELT SHOWERS AND ISOLATED
   THUNDERSTORMS WERE OCCURRING ALONG AN AXIS FROM HOU INTO NRN LA.
   VISIBLE SATELLITE IMAGERY SHOWS TOWERING CUMULUS OCCURRING ALONG THE
   DRYLINE...WHERE STEEP LOW-LEVEL LAPSE RATES ARE AIDING IN STRONG
   BOUNDARY LAYER DESTABILIZATION. UPPER 50S TO LOW 60S DEWPOINTS WERE
   PRESENT AHEAD OF THE CUMULUS LINE...WHICH IS AIDING IN SBCAPE VALUES
   FROM 500-1500 J/KG. 
   
   AS THE EVENING PROGRESSES...THE COLD FRONT WILL CONTINUE TO OVERTAKE
   THE DRYLINE...LEADING TO INCREASING MESOSCALE FORCING FOR ASCENT AND
   AN INCREASED PROBABILITY FOR THUNDERSTORM DEVELOPMENT/COVERAGE.
   HOWEVER...SHORT-TERM MODEL GUIDANCE INDICATES MIDLEVEL HEIGHTS AND
   TEMPERATURES WILL BEGIN TO RISE DURING THE NIGHT...WHICH WILL BE A
   NEGATIVE FACTOR FOR ROBUST DEEP MOIST CONVECTION. THUS...THE SEVERE
   WEATHER THREAT IS CURRENTLY EXPECTED TO BE MARGINAL...MAINLY IN THE
   FORM OF ISOLATED SPORADIC HAIL NEAR 1 INCH IN DIAMETER. IF STORMS
   HAPPEN TO ORGANIZE INTO A LINE...THEN THE POTENTIAL FOR ISOLATED
   DAMAGING WIND GUSTS WOULD INCREASE. CONVECTIVE TRENDS WILL CONTINUE
   TO BE MONITORED.
   
   ..GARNER/EDWARDS.. 02/18/2013
   
   
   ATTN...WFO...LCH...SHV...HGX...FWD...EWX...
   
   LAT...LON   30689730 32109551 31829334 30679320 30079691 30689730