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Mesoscale Discussion 1366
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   Mesoscale Discussion 1366
   NWS Storm Prediction Center Norman OK
   0332 PM CDT Thu Jul 20 2017

   Areas affected...Eastern Montana...western North Dakota...and
   northwestern South Dakota

   Concerning...Severe potential...Watch likely 

   Valid 202032Z - 202130Z

   Probability of Watch Issuance...80 percent

   SUMMARY...An uptick in convective intensity and coverage is expected
   into the evening hours, with hail and damaging wind gusts being the
   primary threats.  A tornado or two may also occur.  A WW issuance
   will be coordinated shortly.

   DISCUSSION...Recent radar/satellite imagery indicate an overall
   increase in convection across the region currently.  Strong
   insolation has fostered 90s F surface temperatures, and steep (8-9
   deg C/km) tropospheric lapse rates, and moderate instability
   (2000-2500 J/kg MUCAPE) ahead of a strengthening dryline (in eastern
   Montana) and along/south of a warm front across northern North
   Dakota.  Recent, more robust convective development has been focused
   along the warm front recently, and higher-based convection across
   southern Montana steadily approaches the dry line currently.

   Models/high-resolution guidance support a continued uptick in
   convection along both the warm front and dry line into the evening,
   with a mix of linear/bowing segments and cellular activity likely. 
   Higher-based convection across southeastern Montana may also
   increase in intensity while approaching slightly better boundary
   layer moisture and stronger buoyancy.  Deep shear profiles favor
   organization (especially from northwestern South Dakota northward
   where stronger mid/upper wind fields exist).  Large hail and
   damaging wind gusts will be the primary threats with intensifying
   activity into the evening hours.  A tornado or two cannot be ruled
   out - especially along the warm front where low-level shear values
   are maximized due to a stout easterly component to the low-level
   flow.

   A severe thunderstorm watch is forthcoming for portions of the
   region.

   ..Cook/Hart.. 07/20/2017

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

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

   LAT...LON   47520600 48090617 48800580 49000491 49010278 48810138
               47880072 46390076 46240090 45460160 44910308 44930421
               45230564 46050627 47200603 47520600 

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Page last modified: July 20, 2017
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