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Mesoscale Discussion 290
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   MESOSCALE DISCUSSION 0290
   NWS STORM PREDICTION CENTER NORMAN OK
   1042 AM CDT MON APR 13 2015

   AREAS AFFECTED...SERN LA

   CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

   VALID 131542Z - 131645Z

   PROBABILITY OF WATCH ISSUANCE...5 PERCENT

   SUMMARY...A TORNADO THREAT MAY PERSIST THROUGH ABOUT 17Z ACROSS FAR
   SERN LA...AND MAY REMAIN CONFINED TO PLAQUEMINES AND ST. BERNARD
   PARISHES...AND ADJACENT COASTAL WATERS.

   DISCUSSION...AT 15Z...NEW ORLEANS WSR-88D HAD SHOWN A PERSISTENT...
   AND PERIODICALLY STRONG...LOW-LEVEL ROTATIONAL COUPLET IN THE MIDDLE
   PORTION OF PLAQUEMINES PARISH...AND HAS SINCE WEAKENED.  THIS STORM
   HAD DEVELOPED AHEAD OF A BAND OF TSTMS WHICH ARCED SEWD FROM
   EAST-CENTRAL THROUGH SERN LA INTO THE GULF OF MEXICO.  A LOCALIZED
   GENERATION AREA FOR STORMS TO DEVELOP PERSISTENT OR QUASI-PERSISTENT
   LOW-LEVEL ROTATIONAL COUPLETS APPEARED TO BE SITUATED NEAR THE
   LAND-SEA INTERFACE OF BARATARIA BAY AND PLAQUEMINES PARISH.  15Z
   MESO-ANALYSIS INDICATED A BOUNDARY EXTENDING WWD FROM 20-30 MILES S
   OF THE COASTS OF WRN FL PANHANDLE...SWRN AL AND SERN MS...AND THEN
   SWWD THROUGH THE MIDDLE PORTION OF PLAQUEMINES PARISH.  THIS
   BOUNDARY THEN EXTENDED NWWD TO 25 SSE OF MSY WHERE IT INTERSECTED
   THE AFOREMENTIONED BAND OF STORMS.  LOCALIZED AREAS OF STRONGER
   LOW-LEVEL CONVERGENCE SHOULD CONTINUE TO BE ASSOCIATED WITH THE
   INTERSECTION OF THE ARCING CONVECTIVE OUTFLOW BOUNDARY AND THE
   SURFACE BOUNDARY...AS THE MAIN BAND OF STORMS SPREADS EWD.  THIS
   WILL SUPPORT A TORNADO POTENTIAL...GIVEN THE PRESENCE OF STRONGER
   LOW-LEVEL SHEAR NEAR THE SYNOPTIC BOUNDARY.  THE ENVIRONMENT ACROSS
   THIS REGION HAS BECOME MODERATELY UNSTABLE WITH EFFECTIVE BULK SHEAR
   CONTINUING TO STRENGTHEN WITH THE EWD PROGRESSION OF A WELL-DEFINED
   MCV ADVANCING ENEWD THROUGH CENTRAL LA.  THIS WILL SUPPORT THE
   SOMEWHAT ORGANIZED ARCING BAND OF STORMS ADVANCING EWD THROUGH SERN
   LA INTO FAR MS.  THE LOW PROBABILITY FOR A TORNADO THREAT SHOULD BE
   RELATIVELY SHORT-LIVED ACROSS FAR SERN LA AND END WITH THE PASSAGE
   OF THE ARCING BAND OF TSTMS.

   ..PETERS/GRAMS.. 04/13/2015


   ATTN...WFO...LIX...

   LAT...LON   29028995 29569000 29788981 29948932 29888890 29108926
               28978956 28928978 29028995 

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Page last modified: April 13, 2015
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