Valid 212000Z – 221200Z
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE DEEP
SOUTH/GULF COAST…
…SUMMARY…
Severe thunderstorms remain possible across the Deep South through
tonight, primarily along the Gulf Coast from southeast Louisiana
into southern portions of Mississippi/Alabama and the Florida
Panhandle. Damaging wind gusts and a couple of tornadoes are
possible.
…20z Update…
The main adjustments to severe probabilities this afternoon has been
to remove the Marginal risk from KY and IN where little
destabilization has occurred due to a combination of limited heating
and ongoing showers for much of the day. The Marginal risk has been
maintained across TN downstream from thin line of low-topped
convection which could still produce some stronger gusts the
remainder of the afternoon. Additional adjustments have been made
on the western periphery of the Marginal risk from middle TN into
southern LA based on effective frontal position and instability
fields.
The Slight risk remains unchanged, with the best chance for severe
thunderstorms expected to continue to be located from southeast LA
into southern MS/AL, southwest GA and the FL Panhandle. The
strongest instability remains along/just offshore the northern Gulf
coast this afternoon, with some northward progression of greater
instability. Backed southeasterly low level flow will continue to
maximize effective SRH, with an increase in SRH with eastward extent
expected through the evening hours as deep layer southwesterly flow
increases with time as the upper trough ejects northeastward. This
will result in a continued tornado threat along the northern Gulf
coast vicinity through tonight. Otherwise, additional thunderstorms
that develop along the eastward-advancing cold front will encounter
a weak instability/strong shear environment. Semi-discrete cells and
bowing line segments in fast moving convection could also pose a
locally damaging wind risk through tonight.
Otherwise, only additional changes have been to the 10% general
thunder area across portions of the Midwest.
..Leitman.. 10/21/2019
.PREV DISCUSSION… /ISSUED 1136 AM CDT Mon Oct 21 2019/
…Deep South/Gulf Coast…
Last night’s extensive/severe-active squall line continues to
exhibit considerable downward organizational and intensity trends
late this morning, with the unperturbed richer warm/moist sector
effectively confined to southern portions of Louisiana/Mississippi
to southwest Alabama and the western Florida Panhandle at late
morning. An MCS is ongoing over the open waters of the Gulf of
Mexico south of Louisiana, with the north edge of this MCS
developing northeastward into coastal southeast Louisiana at this
time. Ascent including a possible MCV related to this squall line
appears likely to focus the most probable severe risk along the Gulf
Coast this afternoon into tonight, in conjunction with moisture-rich
maritime air related to the northward/inland advance of a warm
front. As additional diurnal destabilization occurs and the
warm/moist sector moves northward, strengthening deep-layer flow and
moderately strong low-level shear/SRH will support a mixed
convective mode including supercells and linear bowing segments.
Damaging winds and a couple of tornadoes are possible into tonight
as storms generally transition east-northeastward across the region.
$$