SPC AC 150732

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0232 AM CDT Mon Mar 15 2021

   Valid 171200Z - 181200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE
   EASTERN HALF OF ARKANSAS AND SMALL PORTIONS OF ADJACENT STATES TO
   THE ALABAMA VICINITY...

   ...SUMMARY...
   A broad area of severe weather potential -- including risk for large
   hail, damaging winds, and several tornadoes -- is anticipated
   Wednesday from  the Arkansas/Louisiana vicinity eastward across the
   central Gulf Coast states/southern Appalachians.

   ...Synopsis...
   A vigorous upper low moving across central portions of the U.S. will
   once again be the primary upper feature of interest, as it tracks
   from the Texas/Oklahoma Panhandle vicinity early, to southern
   Missouri through the end of the period.  Ahead of this system,
   moderately strong/accompanying flow will spread across the lower
   Mississippi and Tennessee Valleys and central Gulf Coast states with
   time.

   At the surface, a low is forecast to cross Oklahoma during the day,
   and then should cross the Ozarks through the evening eventually
   reaching the western Illinois vicinity by 18/12Z.  Widespread
   thunderstorms, and substantial/accompanying severe risk, can be
   expected in advance of this system.

   ...The AR/LA vicinity eastward to portions of TN/GA and the FL
   Panhandle...
   Showers and thunderstorms are forecast to be ongoing from Kansas
   southward to Texas ahead of the advancing upper system and
   associated cold front, and eastward across the central Gulf Coast
   states in a zone along a west-to-east warm front.  Some ongoing
   severe risk will likely exist at the start of the period.

   With time, as moisture streams northward from the Gulf of Mexico
   beneath steepening lapse rates, modest heating will push
   surface-based CAPE into the 1000 to 2000 J/kg range with a broad
   warm sector stretching from the AR/LA vicinity eastward to the
   southern Appalachians.  Convection is forecast to increase in
   response to the destabilization, as persistent UVV occurs not only
   in the vicinity of the cold and warm fronts, but also more broadly
   within the general warm-advection regime.

   Southerly low-level flow, veering and increasing to around 50 kt
   from the west/southwest at mid levels will provide shear favorable
   for supercells.  Additionally, ample low-level shear is expected to
   evolve through the day -- particularly near the aforementioned warm
   front which should drift northward across Arkansas and align
   west-northwest to east-southeast from far southern MO to central GA
   by early evening.  As such, tornado risk may be maximized near this
   boundary -- across the AR area during the day, and then later
   increasing eastward across AL and perhaps into GA as well, as
   low-level flow increases into the evening/overnight.  

   In addition to tornado potential -- including the risk for a couple
   of significant tornadoes across a broad area represented by the
   ENH/30% risk area, large hail and damaging winds will also occur in
   some areas.  Risk will continue through the overnight hours,
   tapering from west to east across the lower Mississippi Valley but
   continuing across the central Gulf Coast states and into the
   southern Appalachians through 18/12z.

   ..Goss.. 03/15/2021

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