SPC AC 200555

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1255 AM CDT Wed Sep 20 2023

   Valid 211200Z - 221200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
   CENTRAL AND SOUTHERN HIGH PLAINS...SOUTHERN PLAINS...AND THE
   ARKLATEX...

   ...SUMMARY...
   At least isolated strong to severe thunderstorms are possible across
   portions of the Plains toward the Arklatex Thursday into Thursday
   night.

   ...Synopsis...
   A broad upper-level trough will become established across the
   Interior West tomorrow/Thursday. Multiple mid-level perturbations
   will pivot around the upper trough, with at least one lead impulse
   ejecting into the Plains states by Thursday afternoon. A surface low
   will intensify over the central High Plains in response to the
   approach of this lead impulse, supporting backed surface winds and
   northwestward low-level moisture advection. Mid-level cooling atop
   returning low-level moisture will foster increasing instability
   across the Plains states, in tandem with some deep-layer ascent.
   Scattered strong to severe storms may manifest in this regime from
   the central/southern High Plains to the Arklatex.

   ...Central High Plains to the central Plains...
   Increased low-level convergence should occur during the afternoon
   due to surface low development and associated upslope/moistening
   low-level flow across the central High Plains. Upper 50s to near 60
   F surface dewpoints beneath 8 C/km mid-level lapse rates will
   support 2000-3000 J/kg SBCAPE by afternoon peak heating. At the same
   time, southeasterly surface winds will be overspread by a 25-35 kt
   southwesterly 850 mb jet and westerly 500 mb winds at similar
   magnitudes, resulting in curved and elongated hodographs with 35-45
   kts of effective bulk shear. Some convective inhibition will be
   present through the afternoon, and when considering modest forcing
   for ascent, widespread severe storm coverage becomes questionable.
   Nonetheless, at least some diurnal development is likely in the form
   of isolated supercells capable of severe hail and wind. Some upscale
   growth into an MCS is possible along the low-level jet terminus in
   NE Thursday night, with a couple of severe gusts possible. Greater
   severe probabilities may be needed in future outlooks if denser
   storm coverage becomes apparent.

   ...Southern Plains...
   The ejection of a lead mid-level impulse across the southern Plains
   will support strengthening west-southwesterly low-level flow and
   associated warm-air advection during the late morning or early
   afternoon time frame. Some of the latest high-resolution guidance
   depicts the development of scattered strong thunderstorms, with
   upscale growth into an MCS possible somewhere along the Red River.
   Should this development occur, a couple instances of severe hail
   will be possible given steep mid-level lapse rates, though
   relatively dry air in the low to mid-levels (as shown in some
   forecast soundings) may also encourage a couple of severe gusts.
     
   ...Southern High Plains... 
   Modest surface heating will encourage surface temperatures to warm
   well into the 80s F. With low 50s F surface dewpoints, this will
   support the development of a deep, well-mixed boundary layer. Lapse
   rates should be steep through the troposphere. Furthermore, a belt
   of stronger mid-level flow will overspread the southern High Plains
   with the ejection of a lead mid-level impulse, resulting in
   elongated hodographs. Scattered, fast-moving multicellular
   thunderstorms should develop during the afternoon with an attendant
   isolated severe-gust threat.

   ..Squitieri.. 09/20/2023

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