SPC AC 310551

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1251 AM CDT Mon Aug 31 2020

   Valid 311200Z - 011200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHEAST
   MO...WESTERN AR...CENTRAL/EASTERN OK...AND FAR SOUTHEAST KS...

   ...SUMMARY...
   Severe thunderstorms are possible Monday from parts of the Lower
   Missouri River Valley into the southern Plains. Other strong storms
   may occur from the central Carolinas into eastern West Virginia.

   ...Synopsis...
   Shortwave trough currently moving through the northern High Plains
   is expected to continue eastward through the northern Plains and
   Upper MS Valley before pivoting more northeastward into central
   Ontario this evening. Surface low associated with this shortwave
   will move into northwestern Ontario while occluded. Cold front
   attendant to this low is expected to push gradually
   southward/southeastward into the mid MS Valley, lower MO Valley, and
   northern portions of the southern Plains. By this evening, forward
   progression of this front will have slowed considerably as the
   boundary becomes increasingly displaced from its parent upper
   system. 

   In this wake of this first shortwave trough, another shortwave
   trough will drop southeastward through the northern Rockies into the
   Great Basin. Evolution of these two systems will amplify upper
   troughing across the western CONUS while also maintaining the modest
   southwesterly flow aloft from the Southwest into the OH Valley.
   Several convectively augmented shortwave troughs will likely exist
   within this belt of modest southwesterly flow. One of these
   shortwaves is currently over the TN Valley while another is moving
   out of the southern High Plains into the southern Plains. Gradual
   northeastward motion is anticipated with both of these waves.

   ...Southern Plains into the Lower MO Valley and Mid-South...
   Showers and thunderstorms will likely be ongoing from eastern OK
   eastward into the Mid-South at the beginning of the period,
   supported by the modest shortwave currently moving out of the
   southern Plains. Steep mid-level lapse rates will be in place and
   there is a low probability potential for isolated hail and/or a
   damaging wind gust or two. 

   Storms will likely also be ongoing at the beginning of the period
   over the Lower MO Valley ahead of the cold front. Steep mid-level
   lapse rates and modest vertical shear are sufficient for an
   organized severe threat, and most recent model guidance depicts a
   forward-propagating convective line. Both damaging wind gusts and
   hail will be possible within this line as it moves southeastward
   throughout the morning into the early afternoon.

   Redevelopment ahead of the front in the Ozarks vicinity during the
   afternoon seems unlikely given the low probability of sufficient air
   mass recovery in the wake of the convective line. More probable
   location of afternoon convective initiation is along the portion of
   front in OK and northwest TX. Just how much destabilization occurs
   remains a question given the potential for residual cloud cover.
   Strong buoyancy (i.e. MLCAPE 3000+ J/kg) and moderate vertical shear
   (effective bulk shear around 30-40 kt) will be in place, supporting
   severe storms wherever initiation occurs. Damaging downburst winds
   and large hail, including isolated instances of very large hail, are
   possible. Outflow from the Lower MO/Ozarks convective line could
   also act to locally increase tornado potential across northeast OK.

   Thunderstorms are expected to persist through the evening and
   overnight, supported by warm-air advection across outflow from the
   afternoon storms.

   ...Piedmont into the Central Appalachians...
   Showers and thunderstorms will likely be ongoing across portions of
   the central Appalachians early in the period, supported by the
   shortwave trough current moving through the TN Valley. Another
   shortwave trough is expected to approach the region during the early
   afternoon, likely contributing to an increase in overall storm
   coverage. An increase in low/mid-level flow will also accompany this
   second shortwave, with the subsequent increase in vertical shear
   resulting in a relatively greater potential for a few severe storms.
   Instability will be modest but ample moisture will be in place for
   water-loaded downbursts. Vertically veering low-level flow could
   also contribute to the potential for a tornado or two. Persistent
   wedge front will preclude any severe potential farther northeast
   into more of central and eastern VA.

   ..Mosier.. 08/31/2020

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