Storm Prediction Center Aug 6, 2021 1730 UTC Day 2 Convective Outlook

   SPC AC 061730

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1230 PM CDT Fri Aug 06 2021

   Valid 071200Z - 081200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE NORTHERN/CENTRAL PLAINS INTO THE UPPER MISSISSIPPI VALLEY...

   ...SUMMARY...
   Scattered severe storms capable of producing mainly large hail and
   damaging winds gusts will be possible Saturday from parts of the
   northern/central Plains into the upper Mississippi Valley.

   ...Northern/Central Plains into the Upper Mississippi Valley...
   A shortwave trough will move eastward Saturday across the
   northern/central Plains, eventually reaching the upper MS Valley
   late Saturday night. Modestly enhanced mid-level west-southwesterly
   flow should accompany the shortwave trough. At the surface, a low
   should gradually develop eastward across SD through the day, with
   another area of low pressure likely centered over KS. A warm front
   is forecast to extend eastward from the SD low across
   southern/central MN into WI. Upper 60s to low 70s surface dewpoints
   will likely be present across the warm sector south of the warm
   front and east of a weak cold front/surface trough.

   Diurnal heating and steep mid-level lapse rates over much of the
   Plains will likely contribute to MLCAPE of 2000-3000+ J/kg across
   much of central/eastern SD/NE and into parts of MN/IA. The flow at
   mid levels is expected to remain only modestly enhanced (generally
   25-35 kt). Still, veering of the wind profile with height through
   mid levels across this region should support around 25 to locally 40
   kt of effective bulk shear. Early day storms will probably be
   ongoing Saturday morning along/near the warm front in a low-level
   warm advection regime. While this convection may initially be
   elevated, a transition to surface-based storms with some threat for
   strong/gusty winds appears possible by Saturday afternoon. Depending
   on storm mode, a tornado or two may occur with any supercell along
   the warm front given the enhanced low-level shear forecast.

   Farther west, additional storms should form near and south of the
   surface low across SD/NE late Saturday afternoon as ascent
   associated with the shortwave trough overspreads the warm sector
   across the northern/central Plains. Although mid-level lapse rates
   are forecast to be quite steep, deep-layer shear appears marginal
   for supercells. Even so, isolated large hail may occur with any
   initially discrete storms. Tendency should be for convection to grow
   upscale into multiple clusters Saturday evening as a
   south-southwesterly low-level jet strengthens, with more of a
   damaging wind threat with time into the upper MS Valley. Even though
   storm mode may not be overly favorable, a tornado or two still
   appears possible as the low-level strengthens Saturday evening in
   tandem with the low-level jet.

   ...Kansas into the Oklahoma/Texas Panhandles...
   A decelerating cold front will likely serve as a focus for isolated
   to scattered convection by peak heating late Saturday afternoon in a
   narrow corridor from portions of KS into the OK/TX Panhandles. The
   airmass farther east will likely remain capped, which should limit
   storm coverage with eastward extent in KS/OK Saturday night. MLCAPE
   around 1000-2000 J/kg and modest deep-layer shear will probably
   support a few severe storms capable of hail and/or strong wind
   gusts. If storms can form into one or more small clusters, then
   severe/damaging winds may become a greater threat given a deeply and
   well mixed boundary layer. Confidence in scattered storm coverage is
   not high enough to include greater wind probabilities at this time,
   as the better large-scale ascent associated with the shortwave
   trough should remain generally displaced to the north of KS.

   ...Southeastern Virginia into Central/Eastern North Carolina...
   A mid/upper-level trough will advance east-northeastward across the
   Southeast and towards the Mid-Atlantic through the day on Saturday.
   Even though low/mid-level flow is not forecast to be overly strong,
   there may be enough shear to support loosely organized clusters
   across parts of far southeastern VA into central/eastern NC and
   vicinity Saturday afternoon. Modest instability should develop ahead
   of a weak surface front, and any storms that can form in this regime
   may pose an isolated threat for strong/damaging wind gusts. Poor
   mid-level lapse rates should tend to limit updraft strength, and the
   overall severe threat should remain fairly isolated/marginal.

   ..Gleason.. 08/06/2021

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