SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0654 AM CST Sun Dec 10 2023
Valid 101300Z - 111200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE EASTERN CAROLINAS AND SOUTHEASTERN VIRGINIA...AND NEAR THE
NORTHEASTERN GULF COAST...
...SUMMARY...
Damaging gusts and a few tornadoes are possible mainly over portions
of the eastern Carolinas and southeastern Virginia, and the next few
hours near the northeastern Gulf Coast.
...Synopsis...
In mid/upper levels, high-amplitude synoptic troughing will shift
eastward across the eastern CONUS through the period. This will be
influenced substantially by a strong, basal perturbation apparent in
moisture-channel imagery from southern IL across AR to south-central
TX. This feature should assume a less-positive tilt through the day
as it pivots eastward, reaching from eastern KY across AL and the
western FL Panhandle by 00Z. Thereafter, the shortwave trough will
eject northeastward, become more negatively tilted, and after 06Z,
weaken substantially -- reaching eastern VA by 12Z tomorrow.
At the surface, 11Z analysis showed a cold front from western PA
through WV, near TRI, then across eastern/southern AL to the central
Gulf. The front should proceed eastward across the central/southern
Appalachians today. By 00Z, an elongated area of low pressure (and
perhaps one or more discrete, weak lows) should develop along the
front, expected to extend from northern New England to southeastern
PA, then approximately down the Piedmont into southern GA, to the
eastern Gulf. By 12Z tomorrow, a deepening low should consolidate
on the front over or near RI, with the boundary extending across
Atlantic waters to the FL Keys vicinity.
...Southeast CONUS...
A broken band of thunderstorms may continue to pose a threat for a
tornado or two and damaging gusts for a few hours, as it shifts
eastward through the FL Panhandle and southwestern GA, toward a
region of more-stable boundary-layer air over and north of Apalachee
Bay. The TLH sounding at 12Z sampled the eastern rim of the
moist-unstable low/middle-level profiles well, atop a shallow/stable
near-surface layer that may modify somewhat more favorably before
the convection moves through the area. Effective SRH in the 150-200
J/kg range was noted, consistent with recent VWP there, and at Eglin
AFB before flow veered. For near-term concerns, refer to the
remainder of tornado watch 719 and associated mesoscale discussions.
A relative minimum in severe probabilities (though not zero) is
expected over portions of GA into western SC, where only partly
modified, overland trajectories from FL and GA will render inflow-
layer instability weak and marginal, at best. However, as the zone
of strongest deep-layer ascent shifts eastward today, it will
encounter a boundary layer destabilizing from both cloud-muted
overland/diabatic heating and low-level theta-e advection off the
Atlantic. This will ramp up wind and tornado probabilities again,
as thunderstorms reorganize and intensify -- potentially in two
episodes:
1. A zone of strengthening low-level convergence preceding the
original convective band over easternmost SC, eastern NC and parts
of southeastern VA, with activity forming in the warm sector over
water and land and moving north-northeastward;
2. The initial main band of lift/convection reaching the same area
late afternoon into this evening.
In the destabilizing plume, surface dewpoints (already in the low
60s F) should increase to the mid/upper 60s by afternoon as the
over-water airmass continues to modify favorably. Low/middle-level
lapse rates will be modest but sufficient to support MLCAPE in the
500-1000 J/kg range, in an environment of strengthening deep shear
and somewhat enlarged low-level hodographs. A few supercells and
small bows will be possible with the warm-sector convection, amidst
weak forcing but also weak CINH. The main band of convection may
contain embedded supercells and/or LEWP/bowing circulations.
Surface-based buoyancy will decrease northward and narrow in lateral
extent over the Chesapeake Bay/eastern VA/MD region, but with some
severe still possible.
Farther south across FL, a line of thunderstorms ahead of the front
will offer isolated damaging-wind potential as it crosses from the
Gulf into parts of western/northern FL, with some preconvective
buoyancy maintained by veering winds off the Gulf. However, that
veering will reduce vertical shear and convergence with time this
evening, as instability weakens nocturnally, reducing severe
potential eastward and southward over the peninsula.
..Edwards/Gleason.. 12/10/2023
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