MESOSCALE DISCUSSION 1269
   NWS STORM PREDICTION CENTER NORMAN OK
   0711 PM CDT SUN JUN 24 2007
   
   AREAS AFFECTED...PORTIONS WRN SD...EXTREME SERN MT...EXTREME NERN
   WY...SWRN SD.
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 250011Z - 250215Z
   
   HIGH-BASED CONVECTION THAT DEVELOPED ATOP VERY DRY...WELL-MIXED AND
   HOT BOUNDARY LAYER IN WY PRODUCED ESTIMATED SVR GUSTS IN BLACK HILLS
   WITHIN PAST HOUR.  ASSOCIATED ARCHING OUTFLOW BOUNDARY...IN
   TURN...CONTINUES TO DRIVE ADDITIONAL CONVECTIVE DEVELOPMENT NEWD
   ACROSS PORTIONS BLACK HILLS OF WY/SD.  AS THIS FEATURE MOVES NEWD
   TOWARD MORE FAVORABLE BOUNDARY LAYER MOISTURE...OVERALL ORGANIZATION
   AND SVR THREAT MAY INCREASE OVER PORTIONS WRN SD...NRN PORTION OF
   WHICH MAY REACH ND BORDER DURING NEXT 3-4 HOURS.  ADDITIONAL/MORE
   ISOLATED TSTM DEVELOPMENT APPEARS UNDERWAY ACROSS SRN MEADE COUNTY
   SD -- NE RAP.
   
   SFC MESOANALYSIS SHOWS DOUBLE DRYLINE STRUCTURE ACROSS REGION --
   WITH WRN DRYLINE PUNCHING INTO BLACK HILLS REGION AND DENOTING ERN
   EDGE OF VERY DRY/DOWNSLOPE FLOW ORIGINATING IN WY MOUNTAINS.  ERN
   DRYLINE -- ARCHING N-E OF BLACK HILLS ACROSS PORTIONS
   BUTTE/MEADE/HAAKON/JACKSON COUNTIES...DEMARCATES HOT/WELL MIXED AIR
   MASS WITH 40S F SFC DEW POINTS FROM 50S/60S F DEW POINTS THAT
   CHARACTERIZE NWRN THROUGH CENTRAL SD.  ALTHOUGH MODIFIED RAP RAOB
   AND RUC SOUNDINGS SUGGEST SOME CAPPING REMAINS DOWNSTREAM ACROSS
   REGION...FORCING ATOP OUTFLOW SURGE MAY BE SUFFICIENT TO CONTINUE 
   MUTUALLY REINFORCING FEEDBACK OF COLD-POOL CONVECTIVE INITIATION. 
   DAMAGING WIND WOULD BE PRIMARY THREAT.  HOWEVER...LARGE HAIL ALSO
   MAY BECOME MORE OF A FACTOR AS ACTIVITY ENTERS HIGHER-PW BOUNDARY
   LAYER OF NRN SD...IN ENVIRONMENT WITH LOW LEVEL SHEAR PROFILES AT
   LEAST MARGINALLY FAVORING SUPERCELLS AS WELL AS BOWS.
   
   ..EDWARDS.. 06/25/2007
   
   
   ATTN...WFO...ABR...BIS...UNR...BYZ...
   
   44840469 45490403 46110283 46260164 45420052 44130074
   43670228 43690339 44390317 44780359