LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1241 AM CDT Tue Sep 19 2023
Valid 191200Z - 201200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
SOUTHERN PLAINS...
...SUMMARY...
Scattered severe thunderstorms are possible today and tonight across
portions of the southern Great Plains. Large to very large hail and
severe wind gusts are the primary hazards.
...Southern Plains...
Low-amplitude short-wave trough is currently located over
northeastern NM, shifting east-southeast as it tops the northern
Mexico upper ridge. This feature will eject across the southern High
Plains early in the period, shifting into central OK by 18z. Latest
model guidance suggests a weak disturbance will quickly trail this
feature which will dig southeast across northwest OK during the
early-evening hours.
Latest radar data supports water-vapor imagery with scattered
convection now spreading across the western TX Panhandle, reflecting
the leading edge of large-scale support. This activity should
propagate across western OK early in the period as LLJ responds to
the approaching short wave, focusing into central OK by 18z, then
over northeast OK by 20/00z. With the dryline expected to hold near
-100 longitude, timing of the short-wave trough will be too early
for maximum daytime heating/destabilization. Early-day convection
should limit heating across portions of northern/eastern OK such
that a boundary will be reinforced across this part of the state.
This early-day convection will likely be multi-cellular in nature,
despite the increasing flow/strong deep-layer shear.
Of more concern will be the potential for isolated supercells to
develop in the wake of the lead short wave along the dryline by late
afternoon. Strong surface heating is expected across western OK into
west TX, and convective temperatures should easily be breached near
this boundary by late afternoon. While large-scale forcing should
prove negligible across the High Plains by peak heating, deep
convection should develop within a strongly sheared environment. NAM
forecast sounding at WWR at 23z exhibits MLCAPE in excess of 2000
J/kg, with steep lapse rates through 5 km. While low-level
convergence will likely be weak, a few supercells are expected to
evolve then propagate southeast. Forecast sounding for HBR is
similarly buoyant and any storms that evolve in this environment
should produce hail, some of it possibly exceeding 2" in diameter.
Convection may be more isolated along the trailing dryline into
northwest TX, but strong heating will lead to temperatures warming
into the mid 90s over this region and CINH will prove minimal.
Any storms that develop over northwest OK will track southeast,
possibly along the aforementioned rain-reinforced boundary
downstream. If so, some clustering could occur, especially during
the latter half of the period. Confidence in storm coverage warrants
a continuation of SLGT Risk at this time; however this will be
assessed later this morning for possible changes if necessary.
..Darrow.. 09/19/2023
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