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Mesoscale Discussion 1073
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   MESOSCALE DISCUSSION 1073
   NWS STORM PREDICTION CENTER NORMAN OK
   0304 PM CDT FRI JUN 19 2015

   AREAS AFFECTED...SOUTHERN AND SOUTHEASTERN MONTANA...AND ADJACENT
   PARTS OF NORTHEASTERN WYOMING...AND NORTHWESTERN SOUTH DAKOTA

   CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY 

   VALID 192004Z - 192200Z

   PROBABILITY OF WATCH ISSUANCE...95 PERCENT

   SUMMARY...A FEW THUNDERSTORMS HAVE DEVELOPED IN SOUTHWESTERN MONTANA
   IN THE PAST HOUR...WITH MORE DEVELOPMENT EXPECTED ACROSS WESTERN
   PARTS OF THE MD AREA IN THE NEXT HOUR OR TWO. A TORNADO WATCH IS
   LIKELY WITHIN THE NEXT 1-2 HOURS.

   DISCUSSION...A FEW THUNDERSTORMS HAVE DEVELOPED OVER SOUTHWESTERN
   MONTANA WITHIN THE LAST 1-2 HOURS...WITH ADDITIONAL CUMULUS NOTED
   FARTHER EAST ACROSS SOUTH CENTRAL MONTANA AND NORTHWESTERN WYOMING. 
   OBSERVATIONS AND MODEL GUIDANCE SUGGEST THAT A GRADUAL INCREASE IN
   COVERAGE AND INTENSITY OF THUNDERSTORMS WILL COMMENCE IN THE
   DISCUSSION AREA COINCIDENT WITH 1500-3000 J/KG MLCAPE...SUFFICIENT
   DEEP SHEAR DUE TO 45-50 KNOT FLOW ALOFT...AND GLANCING INFLUENCE OF
   SHORTWAVE CENTERED OVER BRITISH COLUMBIA.  LARGE HAIL AND DAMAGING
   WINDS ARE THE PRIMARY THREATS WITH INITIAL ACTIVITY...BUT THE
   SUPERCELL/TORNADO  AND SIGNIFICANT HAIL THREAT SHOULD INCREASE WITH
   TIME AS LOW-LEVEL SOUTHEASTERLY FLOW STRENGTHENS ALONG WITH
   INCREASED BOUNDARY LAYER MOISTENING/ADVECTION...ESPECIALLY IN
   CENTRAL/EASTERN PARTS OF THE DISCUSSION AREA.  NOCTURNAL
   STRENGTHENING OF THE LOW-LEVEL JET MAY ALSO INCREASE TORNADO THREAT
   TOWARD/JUST AFTER 00Z...ALTHOUGH THIS THREAT WILL BE DEPENDENT
   SOMEWHAT ON HOW LONG STORMS CAN REMAIN DISCRETE AS UPSCALE GROWTH
   INTO A CONVECTIVE COMPLEX IS EXPECTED TOWARD EVENING.  TRENDS ARE
   BEING MONITORED...AND A TORNADO WATCH MAY BE NEEDED PRIOR TO 21Z.

   ..COOK/GUYER.. 06/19/2015


   ATTN...WFO...BIS...UNR...BYZ...GGW...RIW...

   LAT...LON   44930945 45040998 45141039 45371062 45751076 45941060
               46520897 46790758 46770546 46600417 46170298 45420258
               44740272 44180315 43870375 43910482 44070616 44620719
               44840888 44930945 

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Page last modified: June 19, 2015
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