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Mesoscale Discussion 1558
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   MESOSCALE DISCUSSION 1558
   NWS STORM PREDICTION CENTER NORMAN OK
   0919 PM CDT MON JUL 27 2015

   AREAS AFFECTED...PORTIONS OF THE WESTERN DAKOTAS AND EASTERN MONTANA

   CONCERNING...SEVERE THUNDERSTORM WATCH 456...457...

   VALID 280219Z - 280415Z

   THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH
   456...457...CONTINUES.

   SUMMARY...THE SVR RISK CONTINUES IN WWS 456 AND 457.

   DISCUSSION...MULTIPLE CLUSTERS OF STRONG TO SEVERE
   THUNDERSTORMS...WITH A HISTORY OF PRODUCING MEASURED SEVERE WIND
   GUSTS...CONTINUE FROM ERN MT TO THE THE WRN DAKOTAS. SFC ANALYSIS
   INDICATES A FRONTOGENETIC BOUNDARY OVERTAKING THE WRN EXTENT OF
   MODERATE TO STRONG BUOYANCY OVER THE NRN HIGH PLAINS. THIS BOUNDARY
   IS ANALYZED AS A N/S-ORIENTED COLD FRONT FROM THE ERN ONE-QUARTER OF
   MT INTO CNTRL WY...AND IS ACCOMPANIED BY A STRONG PRESSURE RISE-FALL
   COUPLET FROM W TO E ACROSS PARTS OF SRN MT/NRN WY. THIS HIGHLIGHTS
   THE STRONG FORCING FOR ASCENT SPREADING ACROSS THE REGION...WITH THE
   STRENGTHENING ISALLOBARIC WIND COMPONENT ENHANCING BACKGROUND FLOW
   FOR SVR-WIND POTENTIAL WITH CONVECTION...AMIDST 30-45 KT OF DEEP
   SHEAR ENCOURAGING ORGANIZED/SUSTAINED TSTMS. 

   THE BIS AND ABR 00Z RAOBS SAMPLE MODERATE TO STRONG BUOYANCY AND
   LIMITED CAPPING...SUPPORTING CONTINUED EWD/NEWD SPREAD OF THIS
   ACTIVITY...WITH LARGE DCAPE -- OVER 1000 J/KG -- ENHANCING
   DOWNBURSTS AND THEIR PROPENSITY TO MANIFEST STRENGTHENING
   LARGE-SCALE WIND FIELDS AS SVR WIND GUSTS AT THE SFC. RECENT
   MEASURED GUSTS IN THE 50-60-KT RANGE HAVE BEEN REPORTED...AND
   SIGNIFICANTLY SEVERE WIND GUSTS WILL ALSO BE POSSIBLE. CAPPI DATA
   FROM 7 KM INDICATE RENEWED CONVECTION FROM SERN MT TO SWRN SD IN
   ASSOCIATION WITH STRONG DCVA PRECEDING AN UPSTREAM POTENT
   TROUGH...AND ADDITIONAL SVR RISK MAY CONTINUE BEHIND ONGOING
   MULTICELL CLUSTERS.

   ALL OF THIS ACTIVITY WILL CONTINUE SPREADING EWD/NEWD DURING THE
   NEXT SEVERAL HOURS. POLEWARD MASS FLUXES ALONG A TROUGH-PRECEDING
   LLJ -- ALREADY SAMPLED BY ABR/BIS VWPS AS SHOWING 20-30 KT OF FLOW
   IN THE LOWEST 1 KM AGL -- WILL MAINTAIN AN INFLUX OF HIGH THETA-E
   AIR IN THE BOUNDARY LAYER TO MAINTAIN CONVECTION THROUGH THE EVENING
   AND INTO THE OVERNIGHT. SVR POTENTIAL WILL CONTINUE TO ACCOMPANY
   THIS ACTIVITY.

   ..COHEN.. 07/28/2015


   ATTN...WFO...ABR...BIS...UNR...BYZ...GGW...

   LAT...LON   43360336 44190378 45580443 46300531 47560664 48790640
               48910311 48140140 44799971 43430021 43360336 

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Page last modified: July 28, 2015
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