SPC AC 111438

   Day 1 Convective Outlook AMEND 1
   NWS Storm Prediction Center Norman OK
   0938 AM CDT Thu May 11 2023

   Valid 111300Z - 121200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS PARTS OF OK AND
   KS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE LOWER
   MS VALLEY...

   AMENDED FOR LOWER MS VALLEY

   ...SUMMARY...
   Scattered severe thunderstorms are expected this afternoon and
   evening across parts of the Great Plains centered on Kansas and
   Oklahoma. The greatest threat for at least a couple strong tornadic
   supercells should exist across central Oklahoma between 5 to 9 PM
   CDT. Isolated severe storms including a couple of tornadoes are
   possible across the Lower Mississippi Valley.

   ...Central to southern Great Plains...
   A pronounced mid-level low over the Raton Mesa will gradually weaken
   as it drifts into the central High Plains through tonight. This
   weakening trend will result in a moderate LLJ response this evening
   into tonight with pockets of 30-45 kt 850-mb winds. Attendant
   surface cyclone will still diurnally deepen as it similarly drifts
   from the Raton Mesa into southwest KS today. The dryline will mix
   into western OK and arc south-southwest into the Edwards Plateau. A
   north/south-oriented inverted trough/quasi-stationary front will
   extend north to the western Dakotas.

   Dual corridors of thunderstorms are ongoing across a part of
   southeast CO immediately north of the low and lingering farther
   southeast near the northwest TX/southwest OK border. This latter
   area is expected to diminish through midday, resulting in the
   focused ascent region over southeast CO to spread east into western
   KS. Low-topped supercells will become increasingly probable midday
   to early afternoon within a marginally buoyant environment
   initially. A smaller area of supercell development may also form in
   the wake of this activity near the CO/KS border later in the
   afternoon and yield a persistent severe threat into early evening.

   A more volatile supercell environment should develop ahead of the
   dryline in the western to central OK vicinity. A pronounced gradient
   in MLCAPE is likely by late afternoon to early evening as the most
   robust boundary-layer heating post-dryline occurs in TX, while a
   plume of richer moisture advects north ahead of it. This should
   support MLCAPE approaching 1500 J/kg near the OK/KS border to around
   3500 J/kg along the Red River. 

   While a 500-mb jetlet over the southern High Plains will be in an
   overall weakening state, its favorably timed eastward translation
   across the dryline should support sustained supercells. Upper-level
   wind fields will weaken with height and the bulk of hodograph
   structure will consist of enlarged curvature from 0-3 km. This
   suggests supercells should tend towards an HP character with a
   slow-moving cluster type evolution, especially with southern extent
   into north TX. Guidance has a bit more consistency with a moderate
   increase in low-level flow this evening, supporting a strong tornado
   threat with the most intense supercells over central OK. A small
   MCS/embedded supercell cluster will probably persist into eastern OK
   before eventually weakening overnight. 

   ...Lower MS Valley vicinity -- Updated...
   A low-amplitude convectively induced shortwave impulse over the
   Ark-La-Tex will gradually shift east towards the TN Valley through
   tonight. With stronger boundary-layer heating expected towards the
   central Gulf Coast, increasingly broad convective development is
   anticipated into the afternoon ahead of this impulse. Modest
   deep-layer shear will likely prevail across much of the region.
   Still, a few transient supercells and some multicell clustering will
   offer a threat for a couple of mostly brief tornadoes, along with
   sporadic damaging wind gusts and marginally severe hail into early
   evening.

   ..Guyer.. 05/11/2023

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