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Mesoscale Discussion 1159
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   Mesoscale Discussion 1159
   NWS Storm Prediction Center Norman OK
   0726 PM CDT Mon Jun 26 2017

   Areas affected...southeast WA...northern ID...far western MT

   Concerning...Severe potential...Watch unlikely 

   Valid 270026Z - 270130Z

   Probability of Watch Issuance...20 percent

   SUMMARY...Scattered 45-60 kt gusts are likely this evening as a band
   of strong to severe thunderstorms continues to move north-northeast
   across southeastern WA, northern ID, and into far western MT.

   DISCUSSION...Radar imagery over the past few hours has shown a
   gradual upscale growth of convection over northeastern OR.  This
   region is immediately downstream of an approaching upper-level PV
   anomaly moving across northern CA/western OR with a 75 kt 300-mb
   speed max nosing into eastern OR.  9-km CAPPI imagery over the past
   several hours has shown scattered intense thunderstorm cores
   associated with earlier reports of large hail across north-central
   OR.  A 56-kt gust was observed by the Pendleton, OR ASOS at 2347Z
   and a 47-kt gusts by the Walla Walla, WA ASOS at 2311Z.  Surface
   analysis shows temperatures near 100 degrees F over southeastern WA
   and into the lower 90s across northern ID and western MT.  Surface
   dewpoints are in the upper 40-lower 50s---resulting in
   temperature-dewpoint spreads in the 40-50 F range.  

   The very steep lapse rates from the surface through 500 mb will be
   very favorable for evaporative cooling and the propensity of
   scattered strong to severe gusts through the early evening.  There
   was a 8.9 degrees/km 700-500 lapse rate on the 00Z BOI raob with
   40-60 kt southwesterly mid- to high-level flow.  Likewise, the OTX
   00Z raob exhibited steep lapse rates and was substantially moist
   with a PW of 1 inch.  The combination of factors listed above
   coupled with a fairly well organized cold pool/outflow suggests the
   severe threat will persist into western MT and perhaps the Flathead
   Valley later this evening.

   ..Smith.. 06/27/2017

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...MSO...OTX...PDT...

   LAT...LON   46331991 47771808 48181497 47701367 46401363 46021498
               46611655 45911929 46331991 

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