SPC AC 310555

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1255 AM CDT Fri Jul 31 2020

   Valid 011200Z - 021200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
   THE OH/TN VALLEYS INTO THE MID ATLANTIC...

   ...SUMMARY...
   Strong thunderstorms may impact parts of the Ohio and Tennessee
   Valleys Saturday afternoon and evening, accompanied by at least some
   risk for damaging wind gusts and a couple of tornadoes. A few strong
   storms capable of damaging wind will also be possible across parts
   of the Mid Atlantic.

   ...Synopsis...
   A broad upper trough will largely remain in place across the
   central/eastern CONUS on Saturday, with one or more embedded
   shortwaves expected to move northeastward from the mid-MS Valley
   into the OH Valley and lower Great Lakes. An upper ridge will remain
   in place over the West. T.C. Isaias is forecast by NHC to be over
   the Bahamas at the start of the period Saturday morning and move
   north-northwestward to a position offshore of the FL Space Coast by
   Sunday morning. 

   ...OH/TN Valleys...
   Guidance is in generally good agreement depicting a surface low
   moving northeastward from the mid-MS Valley into the OH Valley along
   a nearly stationary front, in conjunction with a convectively
   enhanced midlevel shortwave trough. While midlevel lapse rates will
   be weak, rich boundary-layer moisture and diabatic heating in the
   wake of early convection should result in the development of
   moderate buoyancy near and to the south/east of the low track. 

   Convection should develop or reintensify by early afternoon across
   portions of the TN/OH Valleys. Southwesterly midlevel flow of 35-45
   kt will provide sufficient effective shear for organized convection,
   including the potential for a few supercells. Some enhancement to
   low-level shear/helicity is expected near the surface low and within
   the warm-advection regime near the front extending eastward from the
   low. As a result, some tornado risk may evolve across this region,
   in addition to the threat of locally damaging wind gusts. 

   Considerable uncertainty remains regarding how this scenario will
   evolve, given the impact that multiple rounds of convection from
   Thursday night into early Saturday morning will have on the
   intensity of the midlevel vorticity maximum and associated surface
   low. However, some portion of the Marginal Risk may eventually
   require an increase in tornado and/or wind probabilities once
   details become clearer. 

   ...Mid Atlantic...
   Scattered thunderstorms are expected to develop near and north of a
   northward-moving warm front across portions of the Mid Atlantic
   during the afternoon/evening. Effective shear of 25-35 kt will
   support a few organized multicells and perhaps a weak supercell,
   with locally damaging wind gusts as the primary hazard. 

   ...Central and Southern Rockies/High Plains...
   Northerly midlevel flow around the periphery of the ridge will
   result in a relatively broad region of 30-40 kt effective shear
   across portions of the central/southern High Plains and adjacent
   higher terrain. This will support a conditional threat of organized
   convection with an attendant hail/wind risk, though coverage of
   storms remains highly uncertain outside of the Southern Rockies.
   Probabilities may be eventually needed for some portion of this area
   if confidence in a sufficient coverage of severe storms increases.  

   ...Florida...
   Refer to NHC for the latest updates/forecast regarding Tropical
   Storm Isaias. The current forecast track keeps Isaias east of the
   Florida Atlantic Coast through the end of the period Sunday morning.
   This track would be generally unfavorable for any inland tornado
   risk, so no probabilities have been included at this time.

   ..Dean.. 07/31/2020

   CLICK TO GET WUUS02 PTSDY2 PRODUCT

   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z