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Mesoscale Discussion 425
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   MESOSCALE DISCUSSION 0425
   NWS STORM PREDICTION CENTER NORMAN OK
   1121 AM CDT THU APR 23 2015

   AREAS AFFECTED...SRN LA

   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

   VALID 231621Z - 231745Z

   PROBABILITY OF WATCH ISSUANCE...60 PERCENT

   SUMMARY...INCREASING CONVECTIVE DEVELOPMENT /AND ASSOCIATED SEVERE
   RISK/ ACROSS SRN LA OVER THE NEXT COUPLE OF HOURS SUGGESTS POSSIBLE
   WW ISSUANCE.

   DISCUSSION...LATEST SURFACE ANALYSIS SHOWS A QUASI-STATIONARY FRONT
   LYING ROUGHLY W-E ACROSS SRN LA ATTM...SEPARATING A VERY MOIST GULF
   BOUNDARY LAYER TO THE S FROM A COOLER/DRIER -- AND CONVECTIVELY
   CONTAMINATED -- AIRMASS ACROSS NRN LA AND CENTRAL/NRN MS.

   SCATTERED CLOUD COVER NEAR AND S OF THE FRONT HAS PERMITTED MODEST
   HEATING...WHICH HAS HELPED TO PUSH MIXED-LAYER CAPE VALUES ACROSS
   SRN LA INTO THE 500 TO 1000 J/KG RANGED.  MODIFYING THE MORNING LIX
   /SLIDELL LA/ RAOB FOR CURRENT BOUNDARY LAYER TEMP/DEWPOINT SHOWS
   THAT A WEAK CAP AROUND 900 MB IS NEARLY ERODED -- AND CONVECTIVE
   DEVELOPMENT OVER THE PAST HALF HOUR OR SO JUST N OF LFT /LAFAYETTE
   LA/ WHERE ASCENT IS BEING MAXIMIZED INVOF THE FRONT CONFIRMS THIS
   CAP EROSION.  AS SUCH...EXPECT STORMS TO DEVELOP ACROSS SRN LA INVOF
   THIS FRONT OVER THE NEXT 1-2 HOURS.

   WHILE LOW-LEVEL SHEAR -- EVEN TO THE COOL SIDE OF THE FRONT -- IS
   RELATIVELY WEAK WHICH SHOULD LIMIT ANY TORNADO RISK...RAPIDLY
   INCREASING WLY FLOW WITH HEIGHT THROUGH THE 700 TO 500 MB LAYER IS
   CONTRIBUTING TO DEEP-LAYER SHEAR SUFFICIENT FOR ORGANIZED/ROTATING
   STORMS.  WHILE FLOW ALOFT ALIGNED ROUGHLY ALONG THE FRONT SUGGEST
   THAT CELLULAR STORM MODE WILL LIKELY NOT BE SUSTAINED
   LONG-TERM...LOCALLY DAMAGING WINDS AND HAIL WILL BE POSSIBLE WITH
   ANY STORM/STORM CLUSTER ACROSS THIS REGION.  AS THREAT
   INCREASES...WW ISSUANCE MAY BE NEEDED.

   ..GOSS/GRAMS.. 04/23/2015


   ATTN...WFO...JAN...LIX...LCH...

   LAT...LON   29949295 30279367 30989350 31309276 30939028 30098931
               29528950 29449028 29949295 

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Page last modified: April 23, 2015
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