SPC AC 251243

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0743 AM CDT Mon Mar 25 2024

   Valid 251300Z - 261200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS IN PARTS OF
   EASTERN LOUISIANA AND SOUTHEASTERN ARKANSAS TO EASTERN
   MISSISSIPPI...

   ...SUMMARY...
   Tornadoes and damaging thunderstorm gusts are possible today through
   tonight from east Texas to Alabama.

   ...Synopsis...
   In mid/upper levels, a well-developed synoptic trough extends from a
   cyclone over the central Plains southwestward across far west TX to
   northwestern mainland MX and central Baja.  A series of shortwaves
   behind the leading/synoptic trough will help to maintain larger-
   scale cyclonic flow over much of the western/central CONUS and
   northern MX through the period.  However, the 500-mb cyclone should
   move erratically across KS today into this evening, reaching parts
   of northwestern MO, IA and southern MN by 12Z tomorrow.  To its east
   and south, a broad, strong fetch of cyclonically curving, roughly
   southwesterly flow aloft will shift eastward from the Southern
   Plains across the lower Mississippi, Tennessee and lower Ohio
   Valleys. 

   At the surface, 11Z analysis showed a low near CNK, with Pacific/
   leading cold front having overtaken the dryline and drawn through
   north-central/south-central TX to easternmost Coahuila.  A polar
   front was drawn from the low across northwestern OK, the southern TX
   Panhandle and east-central NM.  The low should move to west-central
   IA by 00Z, with leading front reaching eastern parts of MO/AR,
   northern LA, extreme southeast TX, and the northwestern Gulf.  By
   then, the polar front should extend southward over easternmost parts
   of KS/OK to north-central TX, the northern Permian Basin region of
   TX, and southeastern NM.  By 12Z, the low should reach northwestern
   WI, with the fronts essentially merged southward to western KY, and
   the leading boundary from there across southeastern parts of MS/LA.

   ...East TX to AL...
   A swath of precip and embedded convection -- including widely
   scattered thunderstorms -- is apparent along and ahead of the
   Pacific front, from portions of central TX into the Ozarks.  Much of
   this activity has exhibited a disorganized, anafrontal character for
   several hours, as the leading boundary continues to progress
   slightly rightward of storm motion.  Overall severe potential should
   remain marginal over the next few hours as that general character
   persists.  

   However, severe potential should ramp up from midday onward across
   the outlook area amid favorable/strengthening ambient deep shear. 
   Two processes will contribute to increased surface-based
   convective/severe potential along this boundary from midday into
   tonight:
   1.  Some slowing of the boundary and decrease in anafrontal
   tendencies as it crosses the lower Mississippi River/Delta region,
   and 
   2.  The foregoing warm sector becomes substantially more buoyant
   through a combination of warm advection, moist advection and
   diabatic heating of the boundary layer -- especially from a few
   counties north of I-20 southward.  Forecast soundings reasonably
   depict a northward-narrowing, triangular wedge of 500-1500 MLCAPE
   shifting eastward over the region ahead of the main convective line.
   While much more uncertain, discrete supercell development may occur
   off the southern/southeastern part of the line, given progged
   decrease in MLCINH in the free warm sector. 

   The geometry of the height gradient aloft -- around the southern rim
   of the ejecting cyclone and associated/trailing shortwave trough --
   still will maintain a strongly parallel flow component to the
   primary band of convective forcing, helping to maintain quasi-linear
   mode.  However, given the strength of the deep shear (effective-
   shear magnitudes of 55-65 kt), and of the low-level shear/hodographs
   (effective SRH of 250-500 J/kg), the line will encounter in and near
   the "enhanced" area, tornadoes are probable from associated LEWP/bow
   formations and embedded mesovortices, as well as any supercells that
   can mature enough before/during QLCS merger.  The parameter space
   will support significant (EF2+ damage potential) tornadoes as well,
   though local storm mode/duration will strongly regulate that threat.
   The QLCS gradually will outpace the favorable inflow-layer
   thermodynamic regime from north-south, as it moves eastward into AL
   overnight, but with southern parts still offering a severe threat. 

   ...Lower Missouri Valley region...
   Widely scattered to scattered thunderstorms should form this
   afternoon near the surface low and polar front.  Isolated,
   marginally severe hail or gusts may be noted, and a tornado is
   possible.  

   The airmass between the leading and polar fronts will remain
   somewhat moist, with surface dewpoints in the 50s F over much of the
   region.  Diabatic heating and warm advection will contribute some
   low-level destabilization, though its duration and strength will be
   limited within a narrow corridor northwest of the cloud/precip
   shield from the aforementioned main convective band. However,
   large-scale lift preceding the ejecting mid/upper-level low and
   trough should lead to cold air aloft (e.g., 500-mb temperatures
   around -19 to -22 deg C), steepening low/middle-level lapse rates
   and decreasing MLCINH through much of the afternoon.  This should
   support MLCAPE around 500 J/kg, with strong deep/speed shear and
   potential for vorticity-rich low-level boundaries to augment
   shear/hodographs locally.  Convection should weaken soon after dark.

   ..Edwards/Wendt.. 03/25/2024

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