SPC AC 270828

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0228 AM CST Fri Nov 27 2020

   Valid 291200Z - 301200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE LOWER MISSISSIPPI VALLEY/SOUTHEAST INTO THE CAROLINAS...

   ...SUMMARY...
   Isolated strong to severe thunderstorms may occur Sunday across
   parts of the lower Mississippi Valley into the Southeast and
   Carolinas.

   ...Lower Mississippi Valley into the Southeast and Carolinas...
   A closed upper low over the southern Plains Sunday morning should
   move eastward across the lower MS Valley and Southeast through the
   day. This upper low should begin to merge with a northern-stream
   upper trough over the eastern CONUS Sunday evening into early Monday
   morning. A weak surface low initially near the coast of LA is
   forecast to develop northeastward across the Southeast through the
   day while gradually deepening. Additional deepening of this surface
   low should occur Sunday evening through the end of the period as it
   continues developing northeastward along/near the spine of the
   southern/central Appalachians. A warm front should lift northward
   across parts of the Southeast and Carolinas through the period,
   while a cold front attendant to the surface low sweeps eastward
   across these regions throughout the period.

   A prior frontal intrusion over the northern Gulf of Mexico may tend
   to limit the prospect for substantial inland destabilization across
   the Southeast through Sunday evening. Even so, low to mid 60s
   surface dewpoints should advance northward into parts of southern
   LA/MS/AL and the FL Panhandle in tandem with the developing surface
   low and warm front through the day. Forecast soundings from various
   models suggest weak instability may gradually develop with modest
   daytime heating across these areas along/south of the warm front.
   Strong low-level and deep-layer shear appear likely given the
   enhanced wind field associated with the approaching upper low. This
   high-shear, low-instability setup typically favors isolated strong
   to severe convection across the developing warm sector along/ahead
   of the eastward-moving cold front. Damaging winds a perhaps a couple
   tornadoes would be the main threats with both low-topped supercells
   and linear convection given the forecast strength of the low-level
   flow and shear.

   This isolated severe threat may continue across parts of GA into the
   Carolinas Sunday night and early Monday morning (end of the Day 3
   period), as low-level moisture return occurs from the western
   Atlantic. However, even through the low-level flow across these
   areas should be quite strong, surface-based instability is forecast
   to remain rather weak. Given the potentially limiting factor of
   modest instability, have opted to introduce a broad Marginal Risk
   area from parts of the lower MS Valley/Southeast into the Carolinas.
   The northern extent of any damaging wind/tornado threat remains
   unclear, as there is uncertainty in how far north the low to mid 60s
   surface dewpoints (which will probably be needed for surface-based
   storms) will advance across the Southeast and Carolinas. If
   confidence increases in a narrow corridor of greater instability
   developing across the warm sector, a Slight Risk for damaging winds
   and/or tornadoes may need to be included across some portion of
   these regions in a later outlook update.

   ..Gleason.. 11/27/2020

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   NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0830Z