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Mesoscale Discussion 1766
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   MESOSCALE DISCUSSION 1766
   NWS STORM PREDICTION CENTER NORMAN OK
   0509 PM CDT FRI SEP 26 2014

   AREAS AFFECTED...LOWER CO RIVER VALLEY...SERN CA...FAR SERN NV...WRN
   AZ

   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

   VALID 262209Z - 262315Z

   PROBABILITY OF WATCH ISSUANCE...40 PERCENT

   SUMMARY...AN ISOLATED THREAT FOR LARGE HAIL AND DMGG WIND GUSTS WILL
   EXIST THIS AFTERNOON AND EVENING ACROSS THE LOWER CO RIVER VALLEY
   AND SURROUNDING AREAS. A WW IS POSSIBLE.

   DISCUSSION...SFC ANALYSIS FROM 22Z SHOWED AN AXIS OF MID-60S TO
   LOW-70S F DEWPOINTS ALIGNED ALONG THE LOWER CO RIVER
   VALLEY...CO-LOCATED WITH PW VALUES AOA 1.5 INCHES AND ESTIMATED
   MLCAPE VALUES OF 1500-2500 J/KG /NEAR RECORDS FOR THE DATE/. TSTMS
   WHICH INITIATED WITHIN THE PAST 1-2 HRS HAVE EXHIBITED OCCASIONAL
   POTENTIAL FOR SVR HAIL /PER WDSS-2 MESH ALGORITHM/. STRONG HEATING
   HAS ALSO YIELDED STEEP LOW-LEVEL LAPSE RATES...AND COMBINED WITH THE
   ANOMALOUSLY MOIST AIR MASS...COULD RESULT IN ISOLATED WET
   MICROBURSTS. 

   CURRENT CONVECTIVE TRENDS SUGGEST A SLOW INCREASE IN AREAL COVERAGE
   OVER THE NEXT COUPLE HRS AS STRONGER FORCING FOR ASCENT SPREADS EWD.
   PRIMARY UNCERTAINTY REGARDING WATCH CONSIDERATION IS THE DEGREE OF
   TSTM ORGANIZATION THAT CAN BE ATTAINED...GIVEN 15-20 KT OF
   UNIDIRECTIONAL LOW-MIDLEVEL FLOW AND MODEST EFFECTIVE SHEAR VALUES
   AROUND 20 KT...FAVORABLE FOR PRIMARILY PULSE TO MULTICELL
   CONVECTION. HOWEVER...ORIENTATION OF THE APPROACHING UPPER TROUGH
   SUGGESTS STRONGER MIDLEVEL FLOW WILL GRADUALLY SPREAD EWD ACROSS NRN
   HALF OF THE MCD AREA /MAINLY N OF EED/...ESPECIALLY THIS EVENING AND
   OVERNIGHT. 

   TRENDS WILL CONTINUE TO BE MONITORED FOR A POSSIBLE INCREASE IN
   COVERAGE/INTENSITY OVER THE NEXT COUPLE HRS...WHICH COULD REQUIRE WW
   ISSUANCE.

   ..ROGERS/THOMPSON.. 09/26/2014


   ATTN...WFO...PSR...VEF...

   LAT...LON   36421345 34091358 32401443 32481479 32581560 33701557
               35531552 36491487 36701387 36421345 

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Page last modified: September 26, 2014
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