SPC AC 241728

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1228 PM CDT Wed Mar 24 2021

   Valid 251200Z - 261200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE LOWER MISSISSIPPI VALLEY/MID-SOUTH INTO THE TENNESSEE VALLEY AND
   SOUTHEAST...

   ...SUMMARY...
   The potential for an outbreak of severe storms including several
   long-track strong tornadoes, scattered large to very large hail, and
   severe/destructive winds, will exist Thursday into Thursday evening
   across a portion of the lower Mississippi Valley, Tennessee Valley,
   and Southeast.

   ...Synopsis...
   A shortwave trough with attendant 70-100 kt+ mid-level jet will
   eject northeastward from the southern Plains across the lower/mid MS
   Valley on Thursday, and continue over the OH Valley and lower Great
   Lakes region Thursday night. At the surface, a weak low over
   northeast TX at the beginning of the period Thursday morning is
   expected to likewise develop northeastward to the mid MS Valley
   through the day while deepening. A warm front attendant to this
   cyclone will likely lift northward across the lower MS
   Valley/Mid-South and TN Valley towards the lower OH Valley by
   Thursday evening.

   ...Lower Mississippi Valley and Southeast...
   Storms will likely be ongoing at the start of the period from
   northeast TX into southern AR and northern MS/AL and TN. This
   activity will likely be supported by a southerly low-level jet and
   related warm advection. These storms should shift northward through
   the morning, allowing for destabilization via diurnal heating to
   occur across the lower MS Valley. Rich low-level moisture with at
   least mid to upper 60s surface dewpoints (perhaps lower 70s), should
   advect northward across parts of the lower/mid MS Valley, TN Valley,
   and Southeast by Thursday afternoon. This increasing moisture,
   coupled with diurnal heating, will likely support MLCAPE of
   1500-2000 J/kg developing over a fairly broad portion of these
   regions.

   A pronounced low-level jet (50-60+ kt) will overlie much of this
   region as well, as large-scale ascent from the ejecting shortwave
   trough overspreads the lower/mid MS Valley vicinity. Strongly
   veering and strengthening wind profiles from the surface through mid
   levels will support supercells. 0-1 km SRH along/south of the
   surface warm front will likely reach 300-500 m2/s2, and low-level
   mesocyclones capable of producing strong, long-track tornadoes
   appear likely with any supercells that can form. Scattered large
   hail, some of which may be 2+ inches in diameter, and
   severe/destructive winds also appear probable, both with supercells
   and any bowing line segments that can develop. At this time, the
   best potential for strong tornadoes appears to extend from parts of
   central/northern MS into western/middle TN and central/northern AL,
   mainly Thursday afternoon and evening as storms move generally
   northeastward. Concern does exist regarding the effect of storms
   forming during the morning on the development of instability, and
   potential for destructive interference from too many storms
   developing across the warm sector at the same time. Still, given the
   very favorable environment forecast across this region and the
   potential for numerous supercells, an upgrade to High Risk for
   multiple strong to potentially violent, long-track tornadoes may be
   needed in a later outlook update.

   ...Ohio Valley...
   Fairly widespread precipitation should occur over a majority of the
   lower OH Valley through the day. This should temper diurnal
   destabilization to some degree, but weak instability will probably
   still develop along/east of the surface low and northward-moving
   warm front. At least an isolated severe threat may develop late
   Thursday afternoon into the evening as the southerly low-level jet
   strengthens over this region and low-level moisture increases. The
   potential for a low-topped line of storms capable of producing
   damaging wind gusts and tornadoes will exist given the strength of
   the low-level flow and related shear. These storms will likely be
   tied to a cold front as it tracks northeastward through the evening
   and overnight hours.

   ..Gleason.. 03/24/2021

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