SPC AC 282000

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0300 PM CDT Fri Aug 28 2020

   Valid 282000Z - 291200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE MIDWEST...GREAT LAKES...OH VALLEY...MID-ATLANTIC...AND TN
   VALLEY/SOUTHEAST...

   ...SUMMARY...
   Brief tornadoes and locally damaging winds will remain possible 
   across the Tennessee Valley through this evening. Scattered severe
   thunderstorms are also possible across a broad area of the Great
   Lakes, Midwest, and Mid-Atlantic regions through this evening.

   ...20Z Update...
   In the wake of the morning MCS across WI, clearing skies and
   increasing low-level moisture ahead of a cold front have allowed for
   weak destabilization to occur. However, it still remains unclear
   whether there will be sufficient airmass recovery across WI to
   support severe storms. Have maintained the Slight Risk across this
   area given the uncertainty, but better severe potential may focus
   over Lower MI and central/eastern IA in the short term with
   ongoing/developing convection.

   An isolated strong/gusty wind threat will also continue this
   afternoon with multiple loosely organized clusters extending from
   northern IN into OH and WV. Otherwise, severe probabilities have
   been reduced across parts of western/central PA behind a
   southeastward-moving cluster across southeastern PA. The Slight Risk
   for brief tornadoes and isolated damaging winds across the TN valley
   and vicinity was expanded slightly northward to include more of
   central KY based on recent observational trends.

   ..Gleason.. 08/28/2020

   .PREV DISCUSSION... /ISSUED 1125 AM CDT Fri Aug 28 2020/

   ...Great Lakes to the Corn Belt...
   A non-severe decaying MCS is ongoing in southeast WI. A remnant
   cluster may persist through the afternoon along the northern
   periphery of differential heating near a lingering quasi-stationary
   front. In its wake, abundant cloud coverage and lingering stratiform
   to its north should hamper substantial boundary-layer
   destabilization ahead of the synoptic surface cyclone tracking east
   from northwest WI. Wind profiles will be most favorable for a
   conditional supercell risk across northeast/east-central WI into
   northern/central Lower MI this evening. But uncertainty about
   whether instability can be more than just weak, lowers confidence in
   the amplitude of the threat. Still, have adjusted probabilities to
   indicate a cat 2/SLGT risk for all hazards.

   Farther southwest, convection should attempt to develop along the
   trailing synoptic cold front from central IA to southern WI towards
   early evening. 12Z soundings sampled moderate mid-level lapse rates
   across the region which should hold MLCAPE to between 1500-2000
   J/kg. With the primary forcing for ascent passing to the northeast
   across the central Great Lakes, storm coverage should remain
   isolated to perhaps widely scattered along the front during the
   evening. A few storms will be capable of large hail and damaging
   wind gusts as storms spread into northern IL with coverage expected
   to be consistent with a cat 2/SLGT risk.

   ...TN Valley...
   An arc of lower-topped convection associated with the remnants of
   Laura are ongoing from southwest KY into northeast MS. Modest
   boundary-layer heating is underway in a corridor of broken
   cloudiness ahead of this band, with pervasive cloudiness closer to
   the remnant circulation. A swath of enhanced low-level flow to the
   southeast of the remnant circulation should largely remain confined
   west of where greater boundary-layer destabilization occurs. Still,
   adequate low-level hodograph curvature will exist for lower-topped
   supercells embedded within this leading convective band, likely
   focused across parts of northeast MS, northern AL, and middle TN
   through at least early evening. 

   ...OH to Mid-Atlantic States...
   Ongoing convective clusters across eastern OH into western PA will
   have the potential to intensify as one or more of them shifts east
   of the Appalachians later this afternoon. Boundary-layer
   destabilization is becoming increasingly pronounced east of the
   Appalachians and some CAMs suggest a leading cluster could
   accelerate it spreads towards the Mid-Atlantic coast. This renders
   confidence in increasing the severe risk to cat 2/SLGT here.
   Otherwise, scattered thunderstorms with some congealing into
   multicell clusters are likely across the Upper OH Valley. Scattered
   damaging winds will be the primary hazard across all regions.

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