SPC AC 151245

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0745 AM CDT Sat Aug 15 2020

   Valid 151300Z - 161200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
   INTO EARLY TONIGHT ACROSS PARTS OF THE CENTRAL HIGH PLAINS AND
   NORTHERN MN...

   ...SUMMARY...
   Isolated severe storms capable of large hail and damaging winds will
   be possible over the central High Plains as well as northern
   Minnesota. A more marginal risk for a few severe storms will exist
   from the Great Lakes into the Midwest region.

   ...Synopsis...
   A midlevel high will continue to build over the southern Great
   Basin, with downstream northwesterly flow aloft over the Plains and
   MS Valley.  An initial cold front, associated with a lead shortwave
   trough now moving over WI/western Upper MI, will continue
   southeastward across MO/IL/WI today, and reach IN/Lower MI near the
   end of the period.  Weak ascent along and ahead of the front, in
   combination with modest midlevel lapse rates and boundary-layer
   dewpoints generally in the mid-upper 60s with daytime heating, will
   support scattered thunderstorm development this afternoon into
   tonight.  Deep-layer and low-level vertical shear will be rather
   weak in the warm sector, but the stronger storms could produce
   isolated strong outflow gusts, given DCAPE near 1000 J/kg. 

   Otherwise, an upstream shortwave trough will progress southeastward
   from SK/MB into northern MN this afternoon/evening, with some
   accompanying threat for strong-severe storms.  An upslope flow
   regime across the central/southern High Plains should also support
   widely-scattered thunderstorm development this afternoon into early
   tonight, in a conditionally favorable environment for severe storms.

   ...Central/southern High Plains late this afternoon into tonight...
   Low-level upslope flow is becoming established across the High
   Plains this morning, with low 60s boundary-layer dewpoints spreading
   westward into eastern CO.  Surface heating beneath steep midlevel
   lapse rates will result in moderate-strong buoyancy this afternoon
   (MLCAPE of 2000-3000 J/kg), within a northwest flow regime aloft
   characterized by effective bulk shear of 30-40 kt.  The environment
   conditionally favors splitting supercells, but storm coverage is in
   question given (at best) weak/subtle forcing for ascent from
   southwest NE into eastern CO.  There is also some potential for a
   few storms to persist into tonight across western KS, or additional
   storms could form in a warm advection regime, with a threat for
   isolated large hail/damaging winds.

   Storm coverage should be a little greater across northeast NM in
   advance of an embedded shortwave trough moving south-southeastward
   from southern CO, but weaker vertical shear and CAPE with southward
   extent suggest a marginal wind/hail threat. 

   ...Northern MN this afternoon/evening...
   The left-exit region of an embedded mid-upper speed max over
   southern SK/MB will translate southeastward to northern MN by this
   afternoon/evening.  Boundary-layer dewpoints have been reduced to
   the low 50s across MN in the wake of convection and a cold frontal
   passage yesterday, but cool midlevel temperatures and daytime
   heating should support MLCAPE near 500 J/kg this afternoon. 
   Deep-layer vertical shear will favor supercells, but storm coverage
   is in question given only a diffuse surface trough to focus
   low-level ascent.

   ..Thompson/Gleason.. 08/15/2020

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