SPC AC 220728

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0228 AM CDT Thu Apr 22 2021

   Valid 241200Z - 251200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE SOUTHEAST...

   ...SUMMARY...
   Isolated to scattered severe thunderstorms may occur Saturday across
   parts of the Southeast. All severe hazards appear possible,
   including large hail, damaging winds, and a few tornadoes.

   ...Southeast...
   An upper trough should continue moving eastward from the lower/mid
   MS Valley across the Southeast and Mid-Atlantic on Saturday. A
   strong south-southwesterly low-level jet is forecast to advance
   quickly eastward from AL Saturday morning across GA and into SC by
   the afternoon. At the surface, a weak low over the lower MS Valley
   and Mid-South should develop northeastward towards the central
   Appalachians during the day, with some uncertainty whether it
   deepens substantially or not. Regardless, rich low-level moisture
   should move northward across AL/GA/SC, supporting a threat for
   surface-based thunderstorms.

   Strong to severe convection may be ongoing Saturday morning from
   portions of southern LA into MS and AL in association with the
   low-level jet. As this activity spreads eastward through Saturday
   afternoon, it may continue to pose at least an isolated severe
   threat so long as it does not outpace the low-level moisture return.
   A rather strong mid-level jet attendant to the upper trough will
   support similarly strong deep-layer shear. Forecast soundings across
   the warm sector in GA/SC from both the 00Z NAM and ECMWF show a
   veering/strengthening wind profile with height through mid levels,
   potentially supporting supercells. Some eastward advection of an EML
   from the Plains also appears possible across the warm sector, which
   combined with the increasing low-level moisture and diurnal heating
   should foster moderate to locally strong instability along/south of
   the warm front.

   All severe hazards, including the potential for a few tornadoes,
   appear possible given the favorable thermodynamic and kinematic
   environment forecast as thunderstorms move eastward across the
   Southeast through the afternoon and early evening. The main
   uncertainties are the possible limiting effect of morning convection
   on the development of instability, and predominant storm mode.
   Finally, there also appears to be a conditional threat for severe
   thunderstorms behind the initial morning activity across southern LA
   into MS/AL, as strong instability should develop ahead of an
   eastward-moving cold front. However, low-level flow is forecast to
   quickly veer to westerly behind the passage of the previously
   mentioned low-level jet. This should limit convergence along the
   front, and the most pronounced large-scale ascent associated with
   the upper trough should be mostly east of this region by Saturday
   afternoon. Even so, if convection can develop in this regime, then
   both isolated large hail and damaging winds would be possible.

   ..Gleason.. 04/22/2021

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