LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
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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