Valid 302000Z – 311200Z
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MID
SOUTH TO THE CENTRAL GULF COAST REGION…AND VICINITY…
Isolated damaging winds and a brief tornado remain possible across
parts of the central Gulf Coast States to the Cumberland Plateau
through early morning Thursday.
Current forecast risk areas, and attendant meteorological reasoning,
remain valid at this time, and so no substantive changes to either
appear necessary at this time. Some tweaks to the thunder line have
been made across the Oklahoma vicinity, and a slight eastward
expansion of the MRGL risk (and associated 5% wind/2% tornado
probability areas) has been made over the Florida Panhandle.
Overall however, the severe weather risk — though persisting
through the evening and overnight as the cold front advances —
should remain limited/isolated.
.PREV DISCUSSION… /ISSUED 1126 AM CDT Wed Oct 30 2019/
…Central Gulf Coast to the Cumberland Plateau…
Two primary convective scenarios are apparent through the period. A
leading low-level warm advection regime is supporting a swath of
ongoing showers with embedded thunder from the central Gulf Coast
through AL. A belt of strong low-level flow centered on northern AL
will pivot northeast, becoming increasingly separated from the
gradient of weak buoyancy to the south. Poor mid-level lapse rates
and pervasive stratus should support only meager buoyancy
overlapping where enlarged low-level hodographs can persist. While
it seems unlikely that any of the clusters will have sustained
intensification, a low probability risk for locally strong gusts and
a brief tornado will exist through the afternoon.
Upstream convective development will be tied to an initially weak
warm conveyor region across the Lower MS Valley. Some thinning of
cloud coverage is apparent across southern LA into far southern MS
which should aid in a confined plume of moderate buoyancy (MLCAPE of
1000-1500 J/kg at peak heating). This should aid in late
afternoon/early evening storm development just ahead of a weak
surface cyclone tracking from the Sabine Valley to the Ark-La-Miss.
However, the bulk of strong mid/upper-level flow attendant to a
shortwave trough ejecting from the southern Rockies to the Lower MO
Valley will lag behind the warm sector through mid to late evening.
Cyclogenesis will ensue farther north tonight as tropospheric flow
amplifies. However, stronger shear and forcing for ascent should
remain misaligned north of where the northern extent of weak
surface-based buoyancy can advect across portions of northern MS/AL
to middle/eastern TN. The most likely scenario is still for low
probability coverage of wind/tornado hazards across the Lower MS and
TN Valleys, though the region will be monitored for a possible level
2 categorical risk in later updates.