SPC AC 231252

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0752 AM CDT Mon May 23 2022

   Valid 231300Z - 241200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE SOUTHERN PLAINS...

   ...SUMMARY...
   Severe thunderstorms will be possible today into tonight across
   parts of the southern Plains, with large hail, severe wind gusts,
   and a tornado or two possible.  Isolated damaging wind and a tornado
   may occur across parts of the Southeast.

   ...Synopsis...
   In mid/upper levels, broadly cyclonic flow will cover much of the
   Rockies and Plains, as a series of shortwave perturbations
   contribute to gradual amplification of a slowly eastward-moving
   synoptic trough.  On the southeastern fringe of that regime,
   moisture-channel imagery indicates a weak southern-stream
   perturbation over northeastern Chihuahua and far west TX, east of
   another small trough over western Chihuahua.  The leading feature 
   should move east-northeastward across southwest/west-central TX
   today, with vorticity augmentation likely from convective processes.
   That perturbation should reach eastern OK and east TX by 12Z
   tomorrow.  Meanwhile, behind the southern perturbation and over the
   southern High Plains, height falls will continue as the synoptic
   trough amplifies.  By 12Z, the larger trough should extend nearly
   over the spine of the Rockies from MT-NM, with a prominent vorticity
   lobe over northeastern NM.  Farther east, a deep-layer trough was
   apparent over AL, with weak low-level circulation centered near MGM
   at 11Z.  This feature is forecast to move northeastward across
   northern GA and the western Carolinas through the period, while
   gradually deamplifying.

   At the surface, 11Z analysis depicted a cold front over the Atlantic
   east and south of New England, becoming quasistationary across
   northern/western NC, southeastern TN and northern AL, then a slow-
   moving cold front again over central MS, southern LA, and the
   mid/upper TX coastal-shelf waters.  A quasistationary to warm front
   was drawn from there across south TX to a low near FST.  A separate
   low north of MGM should move northeast and merge with the frontal
   zone through the day.  The TX part of the front will move northward
   and become diffuse, amid an intensifying, broad, low-level warm-
   advection plume.  A dryline should develop today over eastern NM,
   along the western edge of the associated moisture return.  Another
   frontal zone will develop farther northeast by 00Z -- from the
   northern part of a strengthening lee trough/low over northeastern NM
   across the TX Panhandle and north TX.  This boundary should pivot to
   a position from east-central NM to north-central OK by 12Z.

   ...Southern Plains...
   Isolated to scattered thunderstorms are expected to develop this
   afternoon over the High Plains west of the Caprock, as well as over
   a swath of weakly capped, moist boundary layer from the southeastern
   Trans-Pecos/Big Bend regions to the Edwards Plateau and across the
   northern Serranias Del Burro of Coahuila.  The severe threat is not
   well-focused east of the dryline, but with weak MLCINH and variable
   large-scale lift aloft expected, a broad area will have the
   potential for convective initiation and maintenance.

   Large hail and isolated severe gusts will be the main concerns
   during the first few hours of the convective cycle.  Several
   supercells are possible, given strong veering of flow with height,
   and generally 35-45 kt effective-shear magnitudes. Tornado potential
   appears very conditional and relegated to localized boundary/
   storm-scale interactions, given the modest ambient hodographs.  Some
   of the diurnal activity may aggregate into at least a couple loosely
   organized clusters or small MCSs into this evening, supported by
   moisture advection/transport associated with a broad, strengthening
   nocturnal LLJ.  Such convection will offer predominantly a wind
   threat while moving east of the Caprock, and across the
   southwest/south-central TX region.

   A combination of moist/theta-e advection and diurnal heating
   (including heating of higher terrain from the Big Bend region into
   Coahuila) will erode the cap today, and will contribute to favorable
   buoyancy.  By late afternoon, preconvective surface dew points in
   the 50s F should be common from the Panhandles to the South Plains,
   with 60s from the lower Pecos Valley region across the Edwards
   Plateau, Hill Country, north TX, and southern OK.  MLCAPE around
   1000-1500 J/kg will be possible over the High Plains east of the
   dryline, while values of 1500-2000 J/kg may develop prior to
   convective passage from northwest to southwest TX.  Convection
   should weaken with eastward progress tonight over northwest
   TX/southern OK, and near the I-35 corridor in central/south TX.

   ...Southeast...
   Widely scattered to scattered thunderstorms are expected through
   this evening, in a northeastward-shifting, low-level convergence arc
   located east through south of the primary low/middle-level
   circulation center and vorticity max.  A marginal tornado threat is
   apparent from embedded supercell(s)/mesovortices, and isolated gusts
   near severe limits may be noted as well.  The overall coverage and
   magnitude of severe potential still appear isolated and marginal,
   though mesoscale trends will be monitored for better-focused,
   higher-probability potential within this swath.

   The boundary layer should destabilize through the afternoon ahead of
   the primary convergence arc, within a combination of low-level
   theta-e advection and pockets of variably cloud-muted diurnal
   heating.  Although weak midlevel lapse rates will temper buoyancy
   somewhat, moisture associated with surface dew points commonly in
   the mid 60s to lower 70s F will contribute to MLCAPE around 500-1500
   J/kg.  Despite the slow weakening of the deep-layer trough, a
   mesoscale belt of enhanced cyclonic flow in the 850-500-mb layer
   will shift northeastward across GA and parts of the Carolinas
   through this evening, just south through east of the main midlevel
   vorticity lobe.  This will overlie the main low-level convergence
   zone, with enough low-level and deep shear to support sporadic
   organization of associated quasi-linear convection into bows and
   LEWPs.  Occasional, mostly short-lived supercell structures may be
   noted either within the main convective arc, or in discrete to
   semi-discrete supercells to its east.  Some backbuilding or
   regeneration of convection is possible late this afternoon from
   central GA toward southeastern AL and perhaps adjoining parts of the
   FL Panhandle as well, though shear will be weaker over that area by
   then.

   ..Edwards/Kerr.. 05/23/2022

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