SPC AC 120550

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1250 AM CDT Wed Aug 12 2020

   Valid 121200Z - 131200Z

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

   ...SUMMARY...
   Isolated to scattered severe thunderstorms with both large hail and
   strong/damaging winds will be possible today and tonight across
   parts of the northern/central Plains into the Upper Midwest.

   ...Northern/Central Plains into the Upper Midwest...
   A line of storms ongoing across parts of the Dakotas has not been
   well forecast by nearly all 00Z model guidance. With low-level warm
   advection persisting, this convection should continue to spread
   east-southeastward early this morning, and it may produce an MCV by
   the start of the period in MN. Any storms that can remain sustained
   in association with this possible MCV may be capable of producing
   both isolated large hail and strong/gusty winds this morning, mainly
   across parts of western/central MN. Potential redevelopment this
   afternoon over this area remains rather uncertain, but at least an
   isolated severe risk appears possible given the moderate to perhaps
   very strong instability forecast.

   As a large-scale upper trough moves eastward over the Pacific
   Northwest and northern Rockies, other storms should develop later
   this afternoon and evening across the northern High Plains along a
   surface trough. Steep mid-level lapse rates and at least mid to
   upper 60s surface dewpoints are expected to be in place ahead of
   this convection. In tandem with diurnal heating, this will likely
   support the development of moderate to strong instability across the
   Dakotas along/east of the surface trough. Deep-layer shear appears
   somewhat marginal, but it should still be sufficient for organized
   storms capable of producing both large hail and severe wind gusts.
   Upscale growth into an MCS appears possible this evening and into
   tonight, mainly across ND. If this occurs, then severe/damaging wind
   gusts would become the main threat with time across central/eastern
   ND, perhaps continuing into northwestern MN late.

   Additional convection may form this afternoon along the length of
   the lee trough extending southward across much of the central
   Plains. This initial development appears most probable across the NE
   Panhandle/northeastern CO and vicinity as a weak shortwave trough
   moves eastward over the central Plains. The boundary layer
   along/east of the surface trough is forecast to become well mixed,
   and initial high-based storms may be capable of producing both large
   hail and severe downdraft winds. Some clustering/upscale growth
   should occur across western/central NE by this evening as a
   southerly low-level jet strengthens. Damaging winds should become
   the main threat as a MCS moves southeastward into KS this evening
   and potentially continuing overnight.

   ...Lower Mississippi Valley into the Southeast and Mid-Atlantic...
   At least scattered convection is expected this afternoon across a
   broad part of the Southeast into the Mid-Atlantic as a weak
   mid-level low shifts slowly eastward. Although moderate to strong
   instability should develop across much of these regions, both low
   and mid-level flow will be rather weak. Storms should remain
   generally disorganized, and no probabilities for severe wind gusts
   have been included at this time. But, strong/gusty microburst winds
   cannot be ruled out.

   ..Gleason/Squitieri.. 08/12/2020

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