SPC AC 260524

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1224 AM CDT Fri Aug 26 2022

   Valid 271200Z - 281200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF THE UPPER MISSISSIPPI VALLEY...

   ...SUMMARY...
   Isolated severe thunderstorms are possible across the Upper
   Mississippi Valley Saturday afternoon and evening.

   ...Upper MS Valley vicinity...

   A mid/upper shortwave trough will be located over SK/MB and ND/MN
   early Saturday morning. This feature should lift northeast through
   the day. Meanwhile, another mid/upper shortwave trough over the
   central High Plains will develop northeast toward eastern NE/SD and
   western MN/IA by Saturday evening. The initial shortwave trough will
   result in areas of showers/thunderstorms that are expected to be
   ongoing at the beginning of the period near the MN/WI border. Cloud
   cover is expected to linger over the Upper Midwest into parts of the
   central Plains. Nevertheless, temperatures are expected to warm into
   the 80s, with surface dewpoints in the 60s. A plume of steep
   midlevel lapse rates will reside across the region initially, though
   forecast soundings indicate capping through mid/late afternoon. As
   large-scale ascent increases, capping may sufficiently erode such
   that a few surface-based storms could be possible. However, this
   remains uncertain. Regardless of storms being elevated or
   surface-based, forecast hodographs and effective-shear magnitudes
   greater than 30 kt indicate at least marginal supercells will be
   possible. Moderate to strong instability also will support vigorous
   updrafts, with hail and strong gusts being the main hazards. If
   surface-based convection can develop, favorably curved, enlarged
   low-level hodographs and moderate low-level instability suggest some
   tornado potential also is possible. 

   Given uncertainty due to early day convection, persistent cloud
   cover, potential for capping/elevated convection, and storm
   coverage, will maintain the Marginal risk for now, though an upgrade
   to Slight risk may be needed in subsequent outlooks.

   ...Central Plains/Lower MO Valley Vicinity...

   Scattered thunderstorms are expected to develop as the central High
   Plains mid/upper shortwave trough progresses northeast through the
   afternoon. Areas of strong heating and surface dewpoints in the
   low/mid 60s will contribute to modest instability. Weak vertical
   shear will limit storm organization, though steep low-level lapse
   rates and inverted-v sub-cloud thermodynamic profiles suggest some
   strong outflow gusts will be possible. The overall severe threat
   should remain limited from thunderstorm clusters, precluding a
   Marginal risk at this time.

   ...Central MT...

   A compact and intense mid/upper shortwave trough will develop
   east/southeast across the northern Rockies on Saturday. Steepening
   midlevel lapse rates atop poor boundary-layer moisture will support
   at least weak destabilization during the afternoon/evening. Strong
   heating will aid in deep boundary-layer mixing, and inverted-v
   sub-cloud thermodynamic profiles are evident in forecast soundings.
   Increasing midlevel moisture on strengthening southwesterly flow
   ahead of the trough will be sufficient for thunderstorm development
   over the higher terrain of central MT. As this activity spreads
   eastward, occasional strong outflow winds will be possible. Given a
   lack of better-quality boundary-layer moisture (limiting
   instability), and very high-based and shallow convection, overall
   severe potential appears limited/transient.

   ..Leitman.. 08/26/2022

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