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Mesoscale Discussion 689
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   MESOSCALE DISCUSSION 0689
   NWS STORM PREDICTION CENTER NORMAN OK
   0216 PM CDT MON MAY 18 2015

   AREAS AFFECTED...SOUTHWEST TX...FAR SERN NM

   CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 

   VALID 181916Z - 182015Z

   PROBABILITY OF WATCH ISSUANCE...80 PERCENT

   SUMMARY...TSTM INITIATION IS FORECAST TO OCCUR WITHIN THE NEXT 1-2
   HRS PRIMARILY ACROSS THE HIGHER TERRAIN OF SOUTHWEST TX INTO FAR
   SERN NM. PRIMARY THREATS OF LARGE HAIL AND ISOLATED DMGG WIND GUSTS
   ARE EXPECTED...AND TRENDS ARE BEING MONITORED FOR A WW.

   DISCUSSION...VISIBLE SATELLITE IMAGERY SHOWS A FESTERING CU FIELD
   OVER THE DAVIS MOUNTAINS OF SOUTHWEST TX. A TSTM WAS ALSO DEVELOPING
   NEAR THE MEXICAN BORDER JUST E OF BIG BEND NP AND WAS SLOWLY
   ADVANCING NWD. SFC MOISTURE HAS ADVANCED WWD THROUGHOUT THE
   MORNING...WITH MID-50S DEWPOINTS INTO THE ERN TRANS-PECOS REGION AND
   LOW-MID 60S NEAR/E OF FST/6R6. WITH STEEP MIDLEVEL LAPSE RATES
   /7.5-8.5 C/KM/ OBSERVED IN 12Z DRT/MAF SOUNDINGS...MLCAPE VALUES
   CONTINUE TO INCREASE TO 2000-3000 J/KG ACROSS THE REGION. VWP DATA
   SHOWS A DEEP SELY COMPONENT TO 3 KM AGL...VEERING TO WLY IN THE
   MIDLEVELS...YIELDING EFFECTIVE SHEAR MAGNITUDES EXCEEDING 40 KTS.

   TSTM COVERAGE SHOULD CONTINUE TO INCREASE THROUGH THE MID-LATE
   AFTERNOON VIA OROGRAPHIC CIRCULATIONS/OUTFLOW INTERACTIONS AND
   ADDITIONAL DIABATIC HEATING. A FEW SUPERCELLS COULD EVOLVE WITH A
   PRIMARY RISK OF LARGE HAIL AND DMGG WIND GUSTS...WITH THE TORNADO
   THREAT EXPECTED TO BE LIMITED BY WEAK LOW-LEVEL SHEAR AND INCREASING
   T-TD SPREADS INVOF DEVELOPING CONVECTION. CONVECTIVE TRENDS WILL BE
   MONITORED FOR A WW.

   ..ROGERS/THOMPSON.. 05/18/2015


   ATTN...WFO...SJT...MAF...

   LAT...LON   29770476 30930436 32320430 32530388 32580251 32070168
               29740217 29570266 28930307 29270410 29770476 

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Page last modified: May 18, 2015
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