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Mesoscale Discussion 407
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   MESOSCALE DISCUSSION 0407
   NWS STORM PREDICTION CENTER NORMAN OK
   0525 PM CDT SUN APR 17 2016

   AREAS AFFECTED...SOUTH-CENTRAL TX

   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

   VALID 172225Z - 180030Z

   PROBABILITY OF WATCH ISSUANCE...40 PERCENT

   SUMMARY...ADDITIONAL STRONG TO SEVERE STORMS WILL CONTINUE TO
   DEVELOP LATE THIS AFTERNOON INTO THE EARLY EVENING ACROSS
   SOUTH-CENTRAL TX...WITH TRANSIENT SUPERCELLS CAPABLE OF PRODUCING
   LARGE HAIL AND STRONG WIND GUSTS...WHILE A BRIEF TORNADO CANNOT BE
   RULED OUT.

   DISCUSSION...AT 2145Z...MOSAIC AND SINGLE-SITE RADAR IMAGERY SHOWED
   AN ONGOING BROKEN BAND OF STORMS/STORM CLUSTERS EXTENDING FROM
   BLANCO/GILLESPIE COUNTIES SOUTHWARD TO LA SALLE COUNTY.  THESE
   STORMS AND OTHER RECENT STORMS HAVE CONTINUED TO DEVELOP ALONG A
   WESTWARD-MOVING BOUNDARY /LIKELY NOW CONVECTIVELY ENHANCED FROM
   COMPOSITE OUTFLOW BOUNDARIES/ THROUGH A MODERATELY UNSTABLE
   ENVIRONMENT /MLCAPE OF 1500-2500 J PER KG/.  MEANWHILE...GIVEN THE
   SAME THERMODYNAMIC ENVIRONMENT...NEW STORMS ARE EXPECTED TO DEVELOP
   WITH THE CONTINUED MERGER OF THE COMPOSITE WESTWARD-MOVING BOUNDARY
   WITH ANOTHER BOUNDARY EXTENDING FROM NEAR FREDERICKSBURG TO
   KERRVILLE AND WEST OF HONDO IN MEDINA COUNTY TO EASTERN DIMMIT
   COUNTY.  THIS PROCESS HAS ALREADY OCCURRED NEAR FREDERICKSBURG TO
   HONDO.  AFTER THE STORMS FORM WITH THE MERGER OF THE TWO
   BOUNDARIES...NEW DEVELOPMENT THEREAFTER MAY BE LIMITED...AS THE AIR
   MASS IS CONVECTIVELY OVERTURNED/STABILIZED FROM EAST TO WEST. 

   18Z NAM SUGGESTED AN INCREASE IN EFFECTIVE BULK SHEAR INTO THIS
   EVENING...SUPPORTING DEEP ROTATING UPDRAFTS.  THIS COMBINED WITH THE
   AVAILABLE INSTABILITY SUGGESTS ADDITIONAL TRANSIENT STRONG TO SEVERE
   WILL REMAIN A CONCERN INTO THE EARLY EVENING...WITH LARGE HAIL AND
   STRONG WIND GUSTS THE PRIMARY THREATS.  A TORNADO THREAT CANNOT BE
   RULED OUT AS SURFACE TO 850-MB WINDS VEER TO THE SOUTHEAST TO EAST
   WITH THE PASSAGE OF THE WESTWARD-MOVING BOUNDARY.  THIS WILL
   INCREASE THE LOW-LEVEL HODOGRAPH CURVATURE...ENHANCING LOW-LEVEL
   SHEAR.  TRENDS IN RADAR IMAGERY CONTINUE TO SUGGEST STORMS REMAIN
   TRANSIENT /PEAKING IN INTENSITY...THEN WEAKENING/.

   ..PETERS/EDWARDS.. 04/17/2016


   ATTN...WFO...CRP...EWX...

   LAT...LON   28319891 28589940 28969965 29739939 30419904 30479866
               30339836 29649846 28759863 28319891 

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