ACUS01 KWNS 111254
SWODY1
SPC AC 111252
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0652 AM CST Sat Feb 11 2023
Valid 111300Z - 121200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE EASTERN
FLORIDA PANHANDLE ACROSS NORTHERN FLORIDA...
...SUMMARY...
Damaging thunderstorm winds and a couple of tornadoes are possible
from the eastern Florida Panhandle across northern Florida this
afternoon and evening.
...Synopsis...
In mid/upper levels, a progressive, split-flow pattern will persist
through the period, with the splitting features being two similarly
sized cyclones somewhat detached from the prevailing northern
stream. The first -- initially centered over east TX -- is forecast
to move across the southeastern CONUS through the period, with its
center reaching southern MS by 00Z and then turning northeastward
toward northwestern GA by 12Z tomorrow. Associated height falls
already are underway over the northern Gulf and most of the mainland
Southeast, and will spread eastward to the southern Atlantic Coast
and southeastward over the FL Peninsula.
Upstream synoptic-scale ridging aloft -- now over the Rockies --
will deamplify slightly as it moves eastward across the Plains
States, ahead of both a northern-stream perturbation digging
southeastward from northwestern BC across the western Canadian
Prairie Provinces, and the other cyclone -- centered over
northwestern CA at present. The latter's associated 500-mb low will
move south-southeastward along the north-central CA Coast today.
The low then will move obliquely offshore from southern CA by the
end of the period, but with associated cyclonic/difluent flow
spreading across much of northwestern MX and the desert Southwest.
At the surface, a frontal-wave low was evident in satellite imagery
over the northeastern Gulf, roughly south of PNS and west of PIE,
with warm front drawn northeastward to just offshore AAF, then
eastward over the northern FL Peninsula. A cold front extended
south-southwest of the low to the south-central Gulf. The low is
forecast to curl northward over the eastern FL Panhandle and into
extreme southwestern GA or southeastern AL by 00Z, with warm front
eastward across extreme southern GA, and cold front arching across
Apalachee Bay, parts of northwestern FL, just off the west-central
FL coastline, to the east-central Gulf. The initial low should wrap
back and occlude over AL tonight, then move eastward toward western
GA. Meanwhile the triple point should slide eastward over
southeastern GA, then northeastward near the Atlantic Coast,
accompanied by a newer low that should reach the MYR area by 12Z.
At that time, the cold front will have passed offshore from all but
perhaps the immediate coastal areas of south FL along the PBI/FLL/
MIA/HST urban corridor.
...FL Panhandle/North FL and vicinity...
Scattered to numerous showers and widely scattered to scattered
thunderstorms are expected to develop near the cold front over the
northeastern Gulf today, moving inland across the eastern Panhandle
and coastal bend regions of FL. Meanwhile, additional, mid/late-
afternoon convection may form farther east over the northern FL,
focused in a weak-MLCINH environment along residual boundaries from
morning clouds/precip. Wherever sustained/mature storms can access surface-based inflow, supercells and/or small bowing/LEWP segments
are possible, offering damaging gusts and a threat of a couple
tornadoes.
Considerable mesoscale uncertainty still exists regarding the
location and extent of diurnal destabilization and remnant
boundaries behind a plume of precip now moving out of northern FL,
as well as a trailing swath of broken multilayered clouds extending
back across the Gulf. This will influence convective coverage, and
strongly regulate potential for sustained/discrete supercells. As
such, no substantial changes are warranted to the previous outlook,
which remains rather conditional. Mass response to the approaching
cyclone aloft, with the deepening surface low, should lead to
low-level warm advection that can destabilize some areas in the
northern part of the outlook now still under the influence of
earlier outflow/precip -- though favorable destabilization all the
way north to the warm front is quite uncertain. The low's inland
penetration also should outrun the surface-based warm sector inland
into AL/GA. Sufficient diabatic heating and warm advection should
support 500-1000 J/kg preconvective/prefrontal MLCAPE across much,
if not all of the outlook area.
As the day progresses, strengthening deep-layer flow will lead to
greater vertical shear, with forecast soundings indicating 45-55-kt effective-shear magnitudes common across northern FL and the FL/GA
line region by around 21Z. Long, somewhat curved hodographs with
200-300 J/kg effective SRH (most of it in the lowest 1/2 to 1 km)
are possible, suggesting tornado potential with any sustained/
discrete supercells that can form. As the front proceeds eastward
toward the northwestern/west-central peninsular coast early this
evening, associated thunderstorms also may move ashore. Greater
buoyancy is expected, with 1000-1500 J/kg MLCAPE possible, but
weaker deep-layer lift and low-level shear. As such, severe
potential becomes more marginal with southward extent.
...Coastal Carolinas overnight...
As the triple-point low moves past the CHS area, surface-based
buoyancy (which will be greatest over offshore Atlantic waters) may
brush the immediate coastline from there northeastward toward ILM in
the 09-12Z time frame. The buoyancy/shear parameter space favors
supercells in forecast soundings not far offshore. At this time,
too much uncertainty remains to introduce an unconditional outlook
area in that corridor that would link to the early day-2 area for
the southern Outer Banks, but only very minor northward shifts in
progs and/or mesobeta-scale trends would be needed to introduce a
threat. This scenario will be monitored closely throughout the
remainder of the period.
..Edwards.. 02/11/2023
$$
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