SPC AC 261248

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0748 AM CDT Wed Apr 26 2023

   Valid 261300Z - 271200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   NORTH TEXAS AND CENTRAL FLORIDA...

   ...SUMMARY...
   A few tornadoes, along with very large/destructive hail, and severe
   thunderstorm gusts, are expected over parts of north Texas this
   afternoon and evening.  Very large hail and damaging winds also are
   expected over parts of central Florida.

   ...Synopsis...
   The primary mid/upper-level feature influencing this forecast is a
   compact cyclone -- apparent in moisture-channel imagery over the
   southern Rockies and centered near SKX.  A trough extends from the
   low southwestward across southeastern AZ, and northeastward to near
   IML.  The 500-mb low should move southeastward across northeastern
   NM today, then by 00Z, pivot eastward to the TX Panhandle, with
   through southwestward past ELP.  By 12Z, the perturbation should
   devolve to an open-wave trough with primary vorticity lobe over OK,
   and trough across west-central/far west TX.  A broad area of
   difluent, somewhat cyclonic flow will spread across the southern
   Plains to its southeast.  Several embedded, convectively induced/
   reinforced vorticity maxima will eject eastward across the Arklatex
   and Mid-South regions ahead of this feature.

   A continuing fetch of strong upper-level westerlies -- with
   weak/embedded perturbations -- will overlie the northern Gulf and
   FL.  One such weak shortwave trough is apparent over the north-
   central/northeastern Gulf, associated with a few thunderstorms
   southeast of LA.  This feature should reach peninsular FL by this
   evening.

   At the surface, a quasistationary front was drawn at 11Z across
   north-central FL and the northern Gulf, becoming a warm front over
   southeast through central TX, to a low between SWW-LBB.  A cold
   front extended from there southwestward over the lower Pecos Valley.
   The cold front will shift eastward over central/north TX through the
   period, while the warm front shifts northward today to near the DFW
   Metroplex, before being overtaken by convection.  The FL frontal
   segment should remain near its present position.

   ...North TX and vicinity...
   Widely scattered to scattered thunderstorms are expected to occur
   along and south of the warm front this afternoon, with all severe
   modes possible.  The main concern at first may be large to giant
   hail, with ideal conditions progged for generation of hailstones
   above 3 inches in diameter from any sustained supercell(s).  As
   early supercells move east-southeastward to southeastward across the
   region into greater low-level moisture and weak CINH along/south of
   the effective warm front, two processes should occur in tandem:
   1.  Enlargement of low-level hodographs during late afternoon into
   early evening,
   2.  Growth in convective coverage, ultimately leading to a line of
   strong-severe thunderstorms moving southeastward across central and
   northeast TX.  The resulting QLCS this evening will be mainly a
   damaging-wind threat with potential for significant/65+ kt gusts, 
   but with a couple tornadoes and isolated large hail still possible.

   While supercells still are present -- and especially along the warm
   front where low-level shear/vorticity will be maximized -- so will
   be the potential for tornadoes (some possibly capable of
   significant/EF2+ damage).  Uncertainties remain on mesoscale
   specifics of boundary position and mode-transition timing, but both
   giant hail and tornadoes are possible with the boundary potentially
   lying across some part of the Metroplex.  North of the boundary,
   isolated large hail still may occur from the most vigorous elevated
   convection across mainly the Red River region into parts of OK/AR. 
   This includes an ongoing, elevated cluster of thunderstorms over
   northwest TX and southwestern OK, which should move astride the Red
   River across southern OK and parts of north TX through the day.

   A corridor of 2500-3500 J/kg peak/preconvective MLCAPE should
   develop east of the cold front and southwest of the warm front
   through central TX, narrowing northward.  Strong veering of flow
   with height -- especially near the warm front -- will contribute to
   45-60 kt effective-shear magnitudes.  The largest hodograph sizes
   and SRH for surface-based, effective-inflow parcels should be along
   the warm front, but still will favor supercells in the warm sector. 
   Once the modal transition occurs, wind and tornado potential will be
   maximized near embedded mesocirculations and bow/LEWP features.

   ...FL Peninsula...
   Scattered, mainly afternoon to early-evening thunderstorms are
   expected across central and south FL, offering large hail and
   isolated damaging to severe gusts.  The greatest convective coverage
   potential and most-favorable environmental parameter space for
   significantly severe hail appears to be over portions of central/
   east-central FL this afternoon, where supercells with significant
   hail (2+ inches diameter) may occur.  Isolated damaging/severe
   downbursts also may occur, and a tornado is possible with help from
   storm-scale/boundary processes.

   Initial foci for convection will be sea-breeze boundaries near the
   East Coast, and farther inland from the Gulf.  With strong surface
   heating and abundant low-level moisture expected to minimize MLCINH
   by midday, outflow and differential-heating boundaries also may
   support storm initiation throughout the afternoon.  The coldest
   midlevel temperatures and steepest low/middle-level lapse rates are
   expected over central FL, associated with a remnant Mexican EML
   plume.  With surface dewpoints in the upper 60s to low 70s F,
   preconvective MLCAPE should reach 2500-3000 J/kg (locally higher). 
   Low-level flow will be weak, keeping hodographs small for the most
   part.  However, flow will veer strongly with height beneath
   favorable mid/upper winds of the subtropical jet, contributing to
   40-50-kt effective-shear magnitudes.  This, along with boundary
   interactions, will support supercell potential to maximize updraft
   strength and efficiency of hail production.  Hail-growth models
   applied to forecast soundings indicate potential for hailstones 2-3
   inches in diameter, perhaps from multiple storms.  The overall
   convective coverage/intensity should decrease markedly after about
   03Z, when outflow coverage is maximized and nocturnal boundary-layer
   stabilization is underway.

   ..Edwards/Leitman.. 04/26/2023

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