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Mesoscale Discussion 660
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   MESOSCALE DISCUSSION 0660
   NWS STORM PREDICTION CENTER NORMAN OK
   0233 PM CDT FRI MAY 20 2016

   AREAS AFFECTED...PORTIONS OF NORTHERN ALABAMA...AND SOUTH MIDDLE
   TENNESSEE

   CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

   VALID 201933Z - 202200Z

   PROBABILITY OF WATCH ISSUANCE...20 PERCENT

   SUMMARY...A FEW THUNDERSTORMS ARE DEVELOPING IN A SOMEWHAT
   DESTABILIZED AIR MASS AHEAD OF A LIFTING SHORTWAVE TROUGH THAT ARE
   CAPABLE OF PRODUCING MARGINALLY SEVERE HAIL AND WIND GUSTS OVER THE
   NEXT FEW HOURS.

   DISCUSSION...A SMALL AREA OF DESTABILIZATION RESULTING FROM
   AFTERNOON HEATING ON THE NORTHWEST SIDE OF THE GULF-COAST MCS...AN
   INCREASE IN DEEP-LAYER SHEAR ASSOCIATED WITH A SMALL MID-LEVEL
   WESTERLY SPEED MAX...AND SCATTERED THUNDERSTORM DEVELOPMENT IN THE
   VICINITY OF A WEAK SURFACE LOW AND WARM FRONT...IS CONTRIBUTING TO A
   THREAT FOR MARGINAL SEVERE HAIL AND WIND GUSTS IN THE NEXT FEW
   HOURS.  ALTHOUGH MID-LEVEL LAPSE RATES ARE LIKELY RATHER POOR IN THE
   WAKE OF THE MORNING CONVECTION...SURFACE TEMPERATURES HAVE RISEN TO
   THE MID-UPPER 70S WITH SURFACE DEWPOINTS HOLDING IN THE UPPER 60S IN
   A REGION EAST OF THE COLD FRONT AND SOUTH OF THE WARM FRONT
   CONTRIBUTING TO SURFACE-BASED CAPE VALUES OF 500-1000 J/KG. THE
   INITIAL STORMS FROM STARKVILLE MS TO FAR NORTHWESTERN AL HAVE
   EXHIBITED NARROW UPDRAFTS AND WEAK REFLECTIVITIES...POSSIBLY
   INDICATING THAT MID-LEVEL DRY AIR IS BEING ENTRAINED INTO THE
   UPDRAFTS. HOWEVER...ANOTHER HOUR OF HEATING AND THE PROGRESSION OF
   THE STORMS INTO MORE BACKED SURFACE WINDS COULD SUPPORT AN INCREASE
   IN CONVECTIVE INTENSITY OVER THE NEXT HOUR OR TWO...AS INDICATED IN
   RECENT HRRR AND HRRR-PARALLEL RUNS. THE THREAT IS EXPECTED TO
   SUBSIDE NEAR SUNSET AS THE COLD FRONT AND SURFACE LOW COLLIDES WITH
   THE STABLE AIR MASS LEFT OVER FROM THE MORNING CONVECTION.

   ..CONIGLIO/HART.. 05/20/2016


   ATTN...WFO...OHX...BMX...HUN...MEG...JAN...

   LAT...LON   34188838 34538797 34938752 35088739 35258699 35408661
               35328634 35088609 34848604 34538610 34118636 33708659
               33388701 32988763 32918776 32868811 33078844 33708850
               33848846 34188838 

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Page last modified: May 20, 2016
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