ACUS01 KWNS 111241
SWODY1
SPC AC 111239

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0639 AM CST Wed Dec 11 2024

Valid 111300Z - 121200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE EASTERN
CAROLINAS TO SOUTHERN NEW ENGLAND...

...SUMMARY...
Severe thunderstorm winds and a few tornadoes are possible from the
eastern Carolinas to southern New England.  Isolated severe
thunderstorms may occur southward into portions of Florida.

...Synopsis...
Moisture-channel imagery showed a substantial mid/upper trough
extending from a cyclone over the MB/ON border southward over the
Mississippi Valley to a strong, basal shortwave trough over portions
of MS/LA.  The latter feature is forecast to pivot eastward to the
TN Valley and FL Panhandle through 18Z, then turn northeastward
across WV, western VA and the west-central Carolinas by 00Z.  As
that occurs, the entire synoptic trough will become more negatively
tilted, with preceding speed maxima of 160-180-kt at 250 mb, 110-125
kt at 500 mb, and 70-85 kt at 700 mb over parts of the Atlantic
Coast States.

A cold front precedes the main mid/upper trough, and was analyzed at
11Z from east-central PA over western VA to a weak low near AVL,
then across central/southwestern GA and the west-central FL
Panhandle, to the central Gulf.  The front should sweep eastward
across VA, the Carolinas, GA and most of FL today, with a 00Z
position progged from VT across western Long Island, over Atlantic
waters to near or just offshore HSE, then southwestward over more of
the Atlantic to southeastern FL.  The front should proceed offshore
from the remaining Atlantic Coast by around 12Z tomorrow.

...East Coast States...
An ongoing, prefrontal band of convection, with scattered to widely
scattered embedded thunderstorms, was apparent in radar, satellite
and lightning data from the northeastern Gulf northeastward across
the FL Big Bend region and southern/eastern GA.  This activity
should proceed eastward across much of FL and offshore from GA
today, with isolated potential for damaging to severe gusts and/or a
tornado, as it encounters foregoing diabatic surface destabilization
and boundary-layer theta-e advection.  The main changes this cycle
are to the associated "marginal area, to:
1.  Trim on the southwest edge in deference to ongoing convective
trends (faster than earlier guidance), and
2.  Add somewhat more of central/southwestern FL to the
5%-wind/Marginal area to give the trailing part of the main squall
line more room to weaken, as diurnal heating of a moist airmass
somewhat offsets weakening trends in both large-scale and frontal
forcings.

Meanwhile, the most dense potential for damaging to severe gusts is
expected to develop farther north today across central/eastern parts
of the Carolinas, northeastward along the coast into southern New
England.  As the shortwave and synoptic troughs assume negative
tilt, synoptic to frontal-scale lift will increase and overlap,
resulting in a narrow band of convection (some with lightning, but
potentially a majority without) firming up into the Mid-Atlantic and
perhaps southern New England.  The aforementioned deep-layer wind
maxima will contribute to fast embedded cell motions and downward
momentum transfer within this band.  Intense associated gusts
sporadically should penetrate a deeply near-neutral to slightly
above moist-adiabatic layer of lapse rates -- with a shallow
near-surface absolutely stable layer possible -- from around the
Delmarva region northeastward, beneath MUCAPE of around 300-800
J/kg.  Buoyancy will become more surface-based with southern extent
from southeastern VA southward, with the greatest values of
low-level shear/SRH and largest hodographs expected over eastern NC
in and near the area of relatively peaked tornado probabilities.
Line-embedded supercells and/or QLCS mesovortices will be the main
tornado concern, with the wind threat more generalized to any
sustained, bow/LEWP segments within the line.

..Edwards/Jewell.. 12/11/2024

$$

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