Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS02 KWNS 210540
SPC AC 210539
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1139 PM CST Fri Jan 20 2017
Valid 221200Z - 231200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF THE SOUTHEASTERN STATES...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE FL
PANHANDLE TO EASTERN NC...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM AL TO
Widespread thunderstorms, primarily producing damaging winds and a
few tornadoes, are expected across much of the southeastern US
Latest NAM guidance is more in line with other short-range models in
the evolution of a strong upper low as it shifts across the northern
Gulf States and matures over the southern Appalachians during the
latter half of the period. 110kt+ 500mb speed max is forecast to
translate along the Gulf coast into northern FL/southern GA by
23/00z. This feature should encourage a surface low to develop and
lift northeast into northern GA with subsequent deepening expected
as the low moves into the western Carolinas after dark. This is a
potentially significant evolution as a strong LLJ will transport
moisture/instability well inland ahead of the strong upper system.
Latest guidance suggests 12hr 500mb height falls will increase from
180m-240m late in the period and very strong forcing should assist a
well-organized squall line that should develop early then race
northeast ahead of the speed max. Very strong environmental shear
is expected to contribute to damaging wind potential...especially
with fast-moving bow-type structures. While a squall line appears
to be the primary severe mode, there is some concern for tornadoes,
especially if discrete structures develop ahead of the linear MCS.
Farther south across the FL peninsula, while the strongest forcing
will lift north of this region, substantial height falls and a
secondary mid-level speed max will affect the southern peninsula
late. Current thinking is a frontal squall line will easily develop
and progress across the central/southern peninsula by daybreak
Monday. Damaging winds are certainly possible with this convection,
along with a few tornadoes.