SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0655 AM CST Sat Jan 27 2024
Valid 271300Z - 281200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
SOUTHERN ALABAMA AND THE WESTERN/CENTRAL FLORIDA PANHANDLE...
...SUMMARY...
Scattered severe storms are possible today mainly over parts of
Alabama, the Florida Panhandle and coastal Mississippi. Isolated
severe storms may extend into southern Tennessee and the western
Carolinas.
...Synopsis...
The mid/upper-level pattern will remain fairly highly amplified yet
progressive through the period, dominated by strong ridging moving
eastward across western North America, and a downstream trough now
over the southern Plains. The trough -- with an embedded,
intermittently closed 500-mb low over OK -- is forecast to phase
with an initially separate, weaker, northern-stream perturbation
over the Dakotas and northwestern MN. The result should be the
500-mb low's reaching the PAH area by 00Z, along a trough extending
very nearly the length of the Mississippi Valley. Overnight, the
low will move up the lower Ohio Valley, reaching near CVG by the end
of the period, with trough southwestward across MS.
At the surface, the associated low was analyzed at 11Z over
northwestern MS, with cold front arching through central/
southwestern LA and waters offshore from the TX coast. By 00Z, the
low should enter southern KY and approach the position of the mid/
upper-level cyclone center, with cold front across middle TN,
central/southern AL, and the western FL Panhandle. A marine warm
front initially over the northern Gulf will move northeastward over
parts of southern AL and the FL Panhandle today before being
overtaken by convection ahead of the cold front. A slow-moving
synoptic warm front initially was located from the low eastward over
northern parts of MS/AL/GA, and should drift-develop to a 00Z
position across northern GA and the western Carolinas. The front
then should extend near and offshore from the ILM area, with a weak
wave low possible west of CLT. By 12Z, that wave low may be the
occlusion triple point near RDU, with warm front eastward past the
ECG area, and cold front across coastal SC to near a JAX-SRQ line.
...Southeastern CONUS...
Two primary convective episodes with somewhat conditional severe
threats appear plausible today, having some spatial overlap possible
over parts of AL. In chronological order, they are:
1. A prefrontal belt of thunderstorms should move eastward along
the Gulf Coast, likely as an eastward shift of initially poorly
organized activity now located from western AL and southeastern MS
southwestward across southeastern LA. Damaging gusts and a slight
tornado threat may accompany this convection later this morning into
afternoon before it outruns a narrowing sector of favorable
destabilization near the Chattahoochee/Apalachicola Rivers. In the
meantime, some inland expansion/intensification of the convection is
possible today ahead of its downshear precip shield (mainly
southeast of the I-65 corridor in southern AL) as the preceding warm
sector continues to recover from yesterday's MCS across the north-
central/northeastern Gulf. Surface dewpoints across much of the
shelf waters have risen into the upper 60s, with low/mid 70s
detected over open waters of the central Gulf, south of the
decaying/residual outflow boundary. MLCAPE may reach 500-1000 J/kg
in the western FL Panhandle, decreasing considerably northward into
southern AL and eastward toward the coastal bend, amidst 35-45-kt
effective-shear magnitudes.
2. Some severe potential may develop with a low-topped round of
convection forming closer to or along the cold front, this afternoon
over portions of AL and southern/southeastern TN, then moving
eastward across parts of the southern Appalachians. This activity
would occur in a regime of strongly convectively modified boundary-
layer air with marginal moisture (upper 50s to near 60 F surface
dewpoints), thanks mainly to the earlier activity near the coast.
However, midlevel cooling/destabilization, frontal lift, and strong
deep shear (effective-shear magnitudes 50-60 kt) should be present.
Sufficiency of diurnal boundary-layer destabilization behind the
ongoing precip shield remains the greatest uncertainty and potential
limiting factor. Given enough warm advection and/or insolation to
support a few hundred kg of SBCAPE, any sustained cells may rotate,
with damaging gusts and a marginal tornado threat.
..Edwards/Gleason.. 01/27/2024
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