SPC AC 261629

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1129 AM CDT Wed Aug 26 2020

   Valid 261630Z - 271200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER MUCH OF
   LOUISIANA AND OVER PORTIONS OF THE UPPER MIDWEST AND GREAT LAKES...

   ...SUMMARY...
   Hurricane Laura will pose an increasing threat for tornadoes this
   afternoon and overnight across much of Louisiana.  Elsewhere,
   damaging thunderstorm winds and sporadic hail will be possible from
   the Upper Midwest across the Great Lakes.

   ...Hurricane Laura...
   Latest VWP data from KLCH and KLIX have sampled notable 0-1 km SRH
   (150-225 M2/S2) as the expansive wind field north of Hurricane Laura
   impinges on the coast. Thus far, little rotation has been noted with
   outer bands offshore of the LA coast, but an increasing risk for at
   least a few tornadoes will develop late this afternoon and continue
   tonight as higher theta-e air and intense low/mid-level wind fields
   move inland. Higher tornado probabilities may still be warranted for
   tonight in later outlooks as the mesoscale details become clearer.

   ...Upper Midwest/Great Lakes...
   Clusters of thunderstorms continue near and north of a warm front
   that extends from northern MN east across the Upper Peninsula of
   Michigan and then southeast into northern OH, and along a cold front
   over eastern ND. Low-amplitude perturbations within stronger
   mid-level flow, and/or weakening low-level warm advection are
   contributing to the maintenance of these storms. Scattered
   thunderstorms may intensify/redevelop late this afternoon/evening
   along the cold front in the presence of moderate/strong instability
   aided by steep mid-level lapse rates and 35-40 kts of westerly
   mid-level flow. Although some question remains concerning overall
   coverage of the severe threat, large hail and damaging gusts will be
   possible with storms that do develop.  

   Farther east/southeast, thunderstorms may re-intensify near the warm
   front later today across the eastern Great Lakes and into portions
   of western NY/PA aided by impulses within the mid-level flow and
   strengthening warm advection tonight. This area will be on the
   eastern fringes of the EML, despite substantial morning cloud cover
   expect sufficient instability/shear to support multicell clusters
   capable of strong/locally damaging winds.  

   ...Northern Rockies/High Plains...
   Isolated to scattered thunderstorms are expected to develop
   initially this afternoon over the higher terrain in western parts of
   the outlook area, then farther east with time into tonight. A
   surface-based thunderstorm or two also cannot be ruled out over
   lower elevations in the western Dakotas or eastern MT. The
   post-frontal upslope regime of eastern WY, the Black Hills, or the
   NE Panhandle also may contribute to the potential for storm
   initiation. Isolated severe gusts and marginal hail will be
   possible. This thunderstorm potential will be supported by a
   corridor of modest but sufficient low-level moisture and diurnal
   heating behind the western cold front. A well-mixed boundary layer
   will help promote strong/locally damaging downdrafts.

   ..Bunting/Squitieri.. 08/26/2020

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