SPC AC 230558

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1258 AM CDT Thu Apr 23 2020

   Valid 231200Z - 241200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
   FAR EASTERN MISSISSIPPI EAST ACROSS PARTS OF ALABAMA...SOUTHERN
   GEORGIA...NORTHERN FLORIDA AND THE FLORIDA PANHANDLE...TO SOUTHERN
   SOUTH CAROLINA...

   ...SUMMARY...
   Severe thunderstorms are expected across a large portion of the 
   Southeast Thursday through Thursday night, including the potential
   for a few strong tornadoes along with damaging winds and large hail.

   ...Synopsis...
   Between a pair of low-amplitude ridges near the West and East
   Coasts, broadly cyclonic flow aloft will prevail across the U.S.
   through the period.  Within this broad cyclonic regime, a short-wave
   trough is forecast to move steadily eastward across the southeastern
   quarter of the country.  

   At the surface, a low -- initially expected to lie in the vicinity
   of the Ozarks -- will move east into the Tennessee Valley area by
   late afternoon/early evening, and then east-northeastward across the
   central Appalachians.  A trailing cold front will sweep across the
   Southeast, while a wedge/damming front will be slow to retreat
   across the Carolinas.

   ...The Southeast...
   A somewhat complex/messy scenario is unfolding for today, as
   widespread convection currently spreading across the mid and lower
   Mississippi Valley into parts of Tennessee, Mississippi, and Alabama
   will continue moving eastward early this morning.  By 12Z, the
   strongest convection -- including some ongoing risk for severe
   weather -- should extend west-southwestward from east-central
   Alabama to southeast Louisiana.

   As diurnal heating/destabilization occurs ahead of the convection,
   expect storms to intensify -- likely organizing linearly into bands
   of strong/severe storms -- which should sweep across southern
   Georgia and the Florida Panhandle/northern Florida, and southern
   South Carolina through the afternoon.  The storms will be
   accompanied by potential for damaging winds, along with large hail
   and a few tornadoes.  

   Meanwhile, in the wake of this convection, it appears that enough
   clearing/heating will occur across eastern Mississippi and southeast
   Louisiana, and into northern and central Alabama to allow sufficient
   airmass recovery/destabilization to occur.  Up to 1500 to 2500 J/kg
   mixed-layer CAPE may evolve across parts of Mississippi and Alabama,
   and up to 300 to 500 J/kg northward across Tennessee and into
   central and eastern Kentucky.

   As the cold front advances, in conjunction with the short-wave
   troughing aloft, this destabilization will allow new storm
   development to occur by early afternoon -- from east-central and
   southeast Mississippi east into west-central Alabama, and then
   northward across the Cumberland Plateau into Kentucky.  With
   strengthening/veering flow with height providing favorable shear for
   supercells, potential for tornadoes will accompany these storms -- a
   few of which could be strong.  Large hail is also expected, along
   with damaging winds.

   The convection will continue eastward across Alabama, and eastern
   portions of Kentucky and Tennessee through the afternoon, and into
   Georgia.  However, uncertainty with respect to degree of severe risk
   increases with eastward extent across Georgia, due to questions
   regarding the degree of airmass recovery which will have occurred in
   the wake of earlier storms -- likely still ongoing over northern
   Florida.  Still, it appears that fairly substantial all-hazard
   severe risk will extend into at least central Georgia into the
   evening hours, before risk begins to diminish.

   ...Intermountain Region into the Plains...
   Diurnal heating across a large portion of the Intermountain West and
   into the Plains is expected today, beneath broad northwesterly flow
   aloft.  Scant boundary-layer moisture should mix out through the
   afternoon, leaving inverted-v thermal profiles at low levels,
   beneath a couple hundred J/kg high-based CAPE.  Though severe-level
   wind gusts are generally not expected, a few stronger gusts -- aided
   by evaporative enhancment of downdrafts with a few more robust
   storms/storm clusters -- are expected during the afternoon, before
   storms weaken into the evening with the onset of diurnal cooling.

   ..Goss/Lyons.. 04/23/2020

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