Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0749 AM CDT Sat Mar 23 2024
Valid 231300Z - 241200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
SOUTH FLORIDA AND THE KEYS...
...SUMMARY...
Isolated strong to severe thunderstorms may occur today across parts
of south Florida and the Keys.
...Synopsis...
In mid/upper levels, a series of shortwaves -- including the open-
wave remnants of a cyclone now moving toward the Pacific Northwest
Coast -- will contribute to development of a large synoptic trough
over the West by 12Z tomorrow. Meanwhile, a downstream/southern-
stream perturbation -- evident in moisture-channel imagery over the
southern Appalachians to the FL Panhandle and central Gulf -- will
shift eastward. By 00Z, the trough should extend from the Carolinas
and coastal GA south-southwestward across northern FL and the
extreme eastern Gulf. By 12Z, the trough should be offshore from
the southern Atlantic Coast, including FL.
At the surface, 11Z analysis showed a frontal-wave low over
northeastern NC in the RDU/RWI area, with cold front across central
portions of SC/GA to the west-central FL Panhandle and central Gulf.
A prefrontal trough with northwesterly wind shift was drawn across
southern GA, the FL coastal bend, and the east-central Gulf. A warm
front -- poorly defined due to the presence of convection and dense
precip on both sides -- was apparent from the low southeastward over
parts of the Outer Banks. The low should move swiftly northeastward
today, reaching near Montauk Point around 00Z, with the trailing
cold front effectively catching the trough and moving offshore from
the remainder of the Atlantic Coast (including FL).
...South FL/Keys...
Widely scattered to scattered thunderstorms are possible through
midafternoon in the destabilizing, prefrontal warm sector over south
FL. The most vigorous cells may produce marginally severe gusts.
The prefrontal air mass over the region will remain characterized by
surface dewpoints around 68-72 F over most of south FL. Modified
RAOBs and forecast soundings suggest this will support around 1000-
1500 J/kg MLCAPE with minimal CINH, and that convection now over
parts of south FL already may be surface-based in the recovery zone
of warm advection behind the prior night's activity. However, light
and variable winds near the surface will become southwesterly to
westerly through midday, while flow from just above the surface
through 850 mb veers more. Though this will reduce hodograph size
markedly, sufficient speed shear will remain to yield effective-
shear magnitudes around 45-60 kt. Weak/intermittent supercell
characteristics may be noted, while fast cell motions contribute to
locally damaging downdrafts.
...Eastern NC...
Somewhat organized thunderstorms extend from near HSE south-
southwestward over Atlantic waters, moving northeastward. The most-
intense activity should remain offshore where low-level instability
and deep bulk shear each should be most favorable. Persistent
overland precip has minimized buoyancy, and deep shear should
continue to diminish as flow aloft weakens with time nearest the
trough aloft. Behind the early precip area, some destabilization,
related to both warm advection and patchy insolation, is expected
diurnally. This may support isolated to widely scattered convection
along/ahead of the cold front. However, with the low and associated
isallobaric forcing moving quickly away from the region and up the
Mid-Atlantic Coast through 18Z, warm-sector flow will veer, further
reducing both vertical shear and low-level convergence. As such,
unconditional potential appears too low to maintain a severe
outlook.
..Edwards/Grams.. 03/23/2024
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