SPC AC 261730

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1230 PM CDT Fri Aug 26 2022

   Valid 271200Z - 281200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE SOUTHERN/CENTRAL PLAINS INTO THE UPPER MIDWEST...

   ...SUMMARY...
   Isolated strong to severe thunderstorms will be possible Saturday
   across the portions of the southern/central Plains into the Upper
   Midwest. Occasional hail and damaging winds should be the main
   threats.

   ...Southern/Central Plains into the Upper Midwest...
   A low-amplitude upper trough should advance east-northeastward
   across the northern Plains/Upper Midwest into Canada on Saturday. A
   separate shortwave trough over the central Plains should likewise
   develop northeastward into parts of the Upper Midwest through
   Saturday evening. A seasonably moist low-level airmass should be in
   place ahead of both of these features, with a weak front/surface
   trough across the Plains likely delimiting the western extent of any
   appreciable severe risk.

   The potential for organized severe thunderstorms across the Upper
   Midwest, especially MN and vicinity, still appears rather uncertain
   and conditional. The already modest large-scale ascent associated
   with the northern shortwave trough should be shifting into Canada
   through the day, leaving nebulous/unfocused forcing mechanisms for
   convective initiation. This uncertainty is evident in latest CAM
   guidance, which shows varying solutions regarding thunderstorm
   coverage and intensity across MN/WI through Saturday evening. Still,
   the presence of fairly steep mid-level lapse rates and diurnal
   heating should lead to a narrow corridor of at least moderate
   instability developing by late Saturday afternoon. Any thunderstorms
   that can develop across this region despite lingering weak
   convective inhibition would be capable of producing both isolated
   large hail and damaging winds, as effective bulk shear around 35 kt
   promotes some updraft organization.

   A better convective signal exists in guidance across IA and vicinity
   in association with the southern shortwave trough. Similar to
   locations farther north, moderate instability and sufficient
   deep-layer shear should support an isolated hail/wind threat with
   any robust thunderstorms that can develop across the warm sector
   Saturday afternoon and evening. Across the southern/central High
   Plains, isolated to scattered thunderstorms may develop along and
   east of a weak surface front/trough through Saturday afternoon. A
   deeply mixed boundary layer, with inverted-v type forecast
   soundings, should support some threat for isolated severe wind
   gusts. Deep-layer shear this far south appears marginal for any more
   than loose convective organization, but some hail may occur with
   initially more cellular convection before clustering occurs.

   ...Montana...
   A pronounced upper trough with attendant strong mid-level jet is
   forecast to move eastward across the Pacific Northwest and northern
   Rockies on Saturday. Very modest low-level moisture should be in
   place across MT ahead of this feature. While high-based
   thunderstorms should develop off the higher terrain and advance
   eastward across central/eastern MT through Saturday evening, it
   currently appears that instability will remain quite limited.
   Accordingly, have opted to not include low severe wind probabilities
   at this time.

   ..Gleason.. 08/26/2022

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