SPC AC 051943

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0243 PM CDT Sat Sep 05 2020

   Valid 052000Z - 061200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVERNIGHT
   ACROSS PARTS OF SOUTHWEST INTO SOUTH-CENTRAL MN...

   ...SUMMARY...
   Scattered thunderstorms capable of very large hail and isolated wind
   damage are expected tonight across parts of the Upper Midwest.

   ...20z Update...

   The ongoing outlook remains on track and no changes have been made
   with this update. 

   Strong storms may result in briefly strong/gusty winds across parts
   of North Texas this afternoon. A cluster of severe-warned
   thunderstorms south of the DFW Metroplex is tracking northwest
   around 30-35 kt. Velocity data from KFWS radar shows a strong
   northwest surge of thunderstorm outflow, and strong gusts may
   accompany this activity. However, 5 and 7 km CAPPI indicates
   weakening cells, while surface observations show only modest cold
   pool development. As such, any severe threat is expected to be very
   limited in both time and space, and 5% wind probabilities appear
   unnecessary. 

   Otherwise, a cluster/bowing segment is expected to develop later
   this evening and track southeast across southern MN into IA. Very
   large hail and damaging gusts remain the most likely hazard
   associated with this activity.

   ..Leitman.. 09/05/2020

   .PREV DISCUSSION... /ISSUED 1129 AM CDT Sat Sep 05 2020/

   ...Southern MN/IA vicinity overnight...
   An embedded mid-upper speed max near the AB/MT border will crest the
   Great Basin upper ridge and then progress east-southeastward over
   the Dakotas/MN tonight, in advance of an amplifying northern-stream
   trough.  In response, cyclogenesis is expected in the lee of the
   northern Rockies, and a cyclone will subsequently develop eastward
   across the Dakotas tonight.  This will induce a 40-50 kt
   southwesterly low-level jet from the central Plains toward the upper
   MS Valley, which will transport low-level moisture (now across KS)
   northeastward to IA/southern by tonight.  The moistening will occur
   beneath the eastern extent of steep midlevel lapse rates (8-9 C/km)
   with an elevated mixed layer, resulting in moderate-strong buoyancy
   (MUCAPE of 2000-3000 J/kg).

   Strong warm advection on the nose of the low-level jet will likely
   support elevated thunderstorm development tonight (03-06z) near the
   SD/MN border as low-level moisture/buoyancy increase.  Strong
   deep-layer vertical shear and the low-level warm advection will
   result in long, curved hodographs that favor elevated supercells
   with the initial storm development, when very large hail is most
   probable.  Upscale growth into clusters appears likely overnight as
   the storms spread southeastward from MN toward northeast IA. 
   Despite the convection being rooted above the surface, there will be
   some potential for strong downdrafts to reach the surface, with an
   attendant threat for a few damaging gusts.

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