SPC AC 110600

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0100 AM CDT Sat Jul 11 2020

   Valid 111200Z - 121200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF
   THE CENTRAL/SOUTHERN PLAINS INTO THE OZARK PLATEAU AND MID MS
   VALLEY...

   ...SUMMARY...
   Severe thunderstorms with damaging wind and hail are possible on
   Saturday from parts of Kansas and Oklahoma into the lower and mid
   Mississippi Valley. A few strong storms are also possible during the
   afternoon from the coastal Mid-Atlantic into New England with
   isolated damaging wind the main threat.

   ...Synopsis...
   An upper ridge will remain in place across the Southwest into the
   southern Plains today. Around the periphery of the ridge, a
   shortwave trough is forecast to move southeastward from the northern
   Plains into portions of the Midwest and mid-MS Valley. An upper
   trough will remain in place across the East. The remnant circulation
   of T.C. Fay will move quickly into Canada this morning, in advance
   of a shortwave trough moving from the OH Valley into New England. 

   ...Central/southern Plains into the Ozark Plateau...
   Uncertainty remains quite high regarding the evolution of the severe
   threat today into tonight. The key factor will be the potential
   development (or lack thereof) of a southeastward-propagating MCS
   this morning across the central Plains/MO Valley. Most 00Z guidance
   has trended away from developing an extensive early-day MCS, which
   may be due to the stabilizing effects of extensive convection on
   Friday across parts of KS/OK. If this scenario verifies, then the
   primary severe threat will likely be delayed until late afternoon or
   evening across eastern parts of KS/OK into the Ozark Plateau, and
   the magnitude of the severe threat will be greater due to the
   potential for more substantial destabilization prior to the onset of
   the primary threat. Strong instability and effective shear in excess
   of 40 kt would favor the potential for organized convection under
   this scenario, with initial supercells likely growing upscale into
   one or more organized clusters. Significant hail and perhaps a
   tornado would be possible early in the convective evolution, with
   potential for upscale growth and more widespread damaging wind with
   time. 

   Meanwhile, if a more extensive early-day MCS evolves, then the
   primary threat for much of the area may be damaging wind and
   isolated hail associated with the early storms, and a more
   conditional threat late this afternoon or evening along any remnant
   outflow boundaries. 

   Given the uncertainties, a broad Slight Risk has been included with
   this outlook. Some refinement to this area, and possibly an increase
   in probabilities, will be possible in subsequent outlooks as details
   become clearer. 

   Further west into western OK and the TX Panhandle, widely scattered
   thunderstorm development is possible this afternoon within a hot,
   well-mixed environment. Effective shear will be sufficient for some
   updraft organization with any storms in this area. Coverage remains
   uncertain, but a conditional threat for severe wind gusts will be
   present, with steep low-level lapse rates and large DCAPE developing
   by afternoon. 

   ...Midwest/Mid MS Valley...
   The magnitude of destabilization across the Midwest/Mid MS Valley
   will depend to some extent on the evolution of morning convection
   coming out of the central Plains, but at least moderate buoyancy is
   likely to develop by afternoon. Foci for initiation will likely be
   subtle given the nebulous surface pattern, but weak capping and
   large-scale ascent attendant to the shortwave will favor scattered
   thunderstorm development. Unidirectional wind profiles with
   effective shear of 30-40 kt will favor the potential for discrete
   supercells, with an attendant risk of large hail and locally
   damaging wind. 

   ...Northern Mid Atlantic into New England...
   The remnant of T.C. Fay is forecast to move quickly into Canada
   later this morning, but rich low-level moisture and modestly
   enhanced low/midlevel flow should remain in place ahead of the
   shortwave trough moving out of the OH Valley. Scattered thunderstorm
   development is expected by late morning/early afternoon along and
   ahead of a weak surface boundary. The strongest storms will be
   capable of producing locally damaging wind, especially in areas
   where stronger heating and steepening of low-level lapse rates can
   occur.

   ..Dean/Lyons.. 07/11/2020

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