SPC AC 231725

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1225 PM CDT Tue Mar 23 2021

   Valid 241200Z - 251200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE ARKLATEX INTO THE LOWER MISSISSIPPI VALLEY...

   ...SUMMARY...
   Isolated severe thunderstorms will be possible over parts of the
   lower Mississippi Valley and southern Plains, mainly from Wednesday
   evening into the overnight.

   ...Synopsis...
   A lead shortwave trough should advance northeastward Wednesday from
   the Upper MS Valley to the Great Lakes. A separate, low-amplitude
   shortwave trough should also move across parts of the southern
   Plains Wednesday afternoon, in advance of the main upper trough/low
   over northern Mexico and the Southwest that should eject across the
   southern Plains late Wednesday evening/overnight. The primary
   surface low is forecast to develop northeastward across the Upper
   Midwest and Great Lakes through the day. A trailing cold front
   should stall across portions of central/south TX, before lifting
   northward into northeast TX and the lower MS Valley as a warm front
   by Wednesday evening. A convectively reinforced boundary should also
   be in place near the central Gulf Coast at the start of the period
   Wednesday morning. This boundary should also lift slowly northward
   through the day.

   ...Southern Plains into the Lower Mississippi Valley...
   Thunderstorms will likely be ongoing Wednesday morning along the
   central Gulf Coast region, mainly southern LA/MS/AL. This convection
   may continue to pose an isolated/marginal severe threat through the
   morning, but the better severe potential will probably tend to
   remain offshore where greater low-level moisture and related
   instability should be present. Additional thunderstorm development
   across the lower MS Valley and southern Plains along the
   northward-developing warm front appears unlikely through much of the
   day, as a low-level inversion/cap should inhibit robust updraft
   development.

   As the primary upper trough/low moves eastward across the southern
   High Plains late Wednesday, a southerly low-level jet should
   gradually strengthen across parts of central/east TX into the lower
   MS Valley. Elevated instability should increase Wednesday
   evening/night across this region along/north of the surface warm
   front, as somewhat steepened mid-level lapse rates develop eastward
   from the higher terrain of northern Mexico and west TX. Current
   expectations are for isolated strong to severe thunderstorms to form
   near the ArkLaTex region Wednesday evening, and subsequently move
   northeastward towards the Mid-South through the end of the period.
   The presence of 1000-2000 J/kg of MUCAPE and 45-55+ kt of effective
   bulk shear suggest a threat for mainly large hail. A tornado or two
   and occasional strong/gusty winds cannot be ruled out either given
   the strength of the low-level flow/shear. But, this tornado/wind
   threat appears rather conditional at this time, and dependent on
   sufficient low-level moisture to support surface-based storms.

   Farther west, at least weak instability should develop by early
   Wednesday evening across parts of north-central TX into OK. A
   secondary cold front will move eastward across the southern Plains
   late in the wake of the low-amplitude shortwave trough. Isolated to
   perhaps widely scattered storms may develop across parts of
   central/north TX into OK during the evening, where strong deep-layer
   shear and sufficient instability should support a threat for locally
   strong to severe wind gusts and large hail. This isolated severe
   threat may continue through the overnight hours into parts of east
   TX, but uncertainty remains too high regarding surface-based storm
   potential to include a larger Slight Risk area across central/east
   TX at this time.

   ..Gleason.. 03/23/2021

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