SPC AC 231932

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0232 PM CDT Fri Oct 23 2020

   Valid 232000Z - 241200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
   THE GREAT LAKES AND OHIO VALLEY...

   ...SUMMARY...
   Threat for a few severe storms capable of damaging wind, hail and
   perhaps a tornado will continue this afternoon into the early
   evening over a portion of the Great Lakes and Ohio Valley.

   ...Discussion...
   Forecast reasoning as laid out in prior outlooks remains reflective
   of current convective/severe weather evolution across the outlook
   area.  Some minor line adjustments have been made to account for the
   western edge of the outlook areas, to reflect progression of
   advancing convection.  Tweaks have also been made to the slight risk
   area to account for counties currently within WW #501.  Otherwise
   however, Local severe risk will continue across the outlook area
   through early evening.

   ..Goss.. 10/23/2020

   .PREV DISCUSSION... /ISSUED 1120 AM CDT Fri Oct 23 2020/

   ...Great Lakes/OH Valley this afternoon/evening...
   Within the northern stream, a shortwave trough will progress from
   the upper MS Valley to the upper Great Lakes by this evening.  An
   associated surface cyclone in lower MI will gradually deepen and
   move northeastward toward Lake Huron, as a trailing cold front
   translates southeastward across Lower MI, the mid MS Valley, and the
   southern Plains.

   12z regional soundings support the possibility of both low-level
   moisture advection from southwest-to-northeast toward Lower MI in
   advance of the cold front, and downward mixing of moisture from
   aloft with daytime heating.  The net result should be boundary-layer
   dewpoints increasing into the low-mid 60s in southeast Lower MI and
   the upper 60s across the lower OH Valley.  Some weak elevated
   convection is ongoing in the warm sector across the lower OH Valley,
   along the corridor of the low-level jet and where convective
   inhibition is weak for parcels originating near 850 mb.  Additional
   warm sector convection will be possible through the day as the low
   levels destabilize with heating/mixing.  

   The primary focus for thunderstorm development will be the zone of
   ascent along and just ahead of the cold front through the afternoon.
   MLCAPE is expected to range from 1000-2000 J/kg (greatest across the
   lower OH Valley) in advance of the cold front, while low-midlevel
   flow/shear will be stronger toward lower MI.  The net result will be
   an environment favoring bands of storms capable of producing
   damaging winds with sufficiently strong downdrafts and momentum
   transfer.  A tornado cannot be ruled out with embedded rotating
   storms given effective SRH close to 150 m2/s2 and effective bulk
   shear near 35 kt, and marginally severe hail may also occur with
   midlevel lapse rates of 7-7.5 C/km.  The severe threat will diminish
   by late evening across OH as the boundary layer stabilizes and the
   primary shortwave trough passes farther to the north. 

   ...East TX area through this evening...
   Convection has organized as an MCS across north TX this morning with
   a leading convective line and weak MCV.  The downstream environment
   across southeast TX appears conducive to maintaining some form of
   this convection through the afternoon, with the southwest extent of
   the convection limited by more substantial midlevel capping.

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