SPC AC 130556

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1156 PM CST Mon Dec 12 2022

   Valid 131200Z - 141200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF EASTERN TEXAS...LOUISIANA...AND INTO THE LOWER MISSISSIPPI RIVER
   VALLEY...

   ...SUMMARY...
   Severe thunderstorms capable of all severe hazards including
   tornadoes, some strong, are possible from parts of east Texas to the
   Lower Mississippi Valley area today and tonight.

   ...Synopsis...
   An anomalously deep upper-level cyclone centered over the Plains
   states is forecast to shift slowly eastward today and tonight while
   90-100+ kt of mid-level flow overspreads the Mississippi River
   Valley and Gulf Coast. A sub 1000 mb surface low across northern KS
   and southern NE will continue to advect a partially modified Gulf
   airmass inland ahead of a fast moving cold front. Rapid
   destabilization and strong vertical shear beneath a 50+ kt 850 mb
   jet will support a risk for all severe hazards over a wide area from
   early this morning through the overnight hours.

   ...Central OK into central TX ...
   Early in the forecast period a broken band of thunderstorms is
   expected to be ongoing from central OK south toward the I-20
   corridor into central TX. Likely just ahead of the surging Pacific
   front, strong poleward advection of modified Gulf moisture will
   support modest destabilization in the absence of robust surface
   heating. Area RAP soundings show meager MUCAPE around 500 J/kg from
   central OK south toward the Red River vicinity where values increase
   to 1000-1500 J/kg. In combination with sufficient buoyancy, very
   strong shear profiles are expected through the morning hours beneath
   a 50+ kt low-level jet. Storm organization into a broken linear
   band/QLCS with embedded supercell structures appears likely. With
   0-1km SRH in excess of 250-300 m2/s2 damaging wind gusts and
   tornadoes will be possible. Confidence is greatest in a sustained
   severe risk near and south of the Red River valley where the best
   overlap of strong forcing for ascent and surface destabilization is
   expected.

   ...ArkLaTex into the Lower MS River Valley...
   As the main frontal band continues east through the early afternoon,
   strong low-level warm advection is expected ahead of it as a warm
   front lifts north through southeastern OK and into central AR. To
   the south, low to mid 60s F surface dewpoints will stream northward
   reaching the AR/LA border by 21z. Dense stratus cover in the warm
   advection region will likely forestall surface heating, but the
   combination of surface moistening and cooling aloft should result in
   more favorable thermodynamics with time. As the low-level jet shifts
   eastward through the afternoon and evening low-level hodographs
   should expand favorably for supercells capable of all severe
   hazards.

   Storm mode remains somewhat uncertain with weak capping and strong
   warm advection taking place ahead of the frontal band. HREF guidance
   suggests the squall line may reorganize into more semi-discrete
   elements with additional development possible ahead in the warm
   sector with time as better thermodynamics are realized. 0-1km shear
   values in excess of 35 kt will be strongly supportive of low-level
   updraft rotation and some strong tornado risk may evolve if
   semi-discrete supercells are able to develop. Otherwise, embedded
   circulations capable of strong winds and tornadoes are expected.

   The northern extent of the severe risk also remains unclear and tied
   to destabilization with advection of the richer boundary-layer
   moisture. Faster model solutions suggest storms may remain severe
   across portions of northern MS into early Wednesday morning. While
   thermodynamics are likely to be marginal, very strong low and
   mid-level shear profiles will support a mix of supercells and short
   line segments capable of damaging gusts.

   Farther south across southeastern LA and southwest MS, continued
   onshore advection of the moist and unstable Gulf airmass will likely
   keep the severe risk ongoing through the night. Large and mostly
   streamwise low-level hodographs (0-500m SRH 200+ m2/s2) will favor
   supercells and a risk for nocturnal tornadoes.

   ..Lyons/Kerr.. 12/13/2022

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