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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0748 AM CDT Mon Apr 18 2022

Valid 181300Z - 191200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS NEAR THE
ATLANTIC COAST OF FLORIDA AND THE CAROLINAS...

...SUMMARY...
Isolated severe thunderstorms are possible near the Atlantic Coast
of Florida and the Carolinas.

...Synopsis...
The mid/upper-level pattern over the CONUS this period will be
characterized by sharpening troughing/cyclonic flow over the East,
and a less-amplified, cyclonic flow with an open-wave trough moving
ashore on the West Coast.  Moisture-channel imagery indicates a
series of vorticity maxima co*prising a strong trough now evident
from the MB/ON border southeastward to IL.  To its southeast, a
series of weaker perturbations extend across the southern
Appalachians, GA and the Florida coastal bend.  As the northern-
stream trough digs southeastward across the upper Great Lakes and
evolves into a closed, synoptic-scale cyclone, the Southeastern
perturbations will eject offshore from the Carolinas, FL and GA,
while weakening.

The 11Z surface chart depicted a low -- associated with the
southern-stream mid/upper troughing -- near TYS, with cold front
southwestward across west-central AL to southeastern LA and the
middle TX Coast.  The low should deepen and move in a cyclonically
curving, net northeastward path across the central/eastern Carolinas
today, reaching the southern Chesapeake Bay area by 00Z.  The cold
front then should extend across north-central/west-central FL, but
with westerly to northwesterly flow to its southeast over much of
the peninsula.  By 12Z tomorrow, the low should reach southeastern
New England and occlude.  The cold front will clear the entire FL
Peninsula by that time.  A marine front remains offshore from the
coastal Carolinas, and should move northward and somewhat inland,
amidst intensifying low-level warm advection.

...c*astal Carolinas...
Widely scattered to isolated thunderstorms already are evident in
radar, satellite and lightning-detection imagery over the open
Atlantic, roughly near a line from XMR-HSE.  The area of convection
is expected to fill in and expand somewhat westward from that line
toward the coast through the remainder of the morning, with embedded
activity moving northeastward to north-northeastward.  Some elements
in the northern part of the convective plume may cross the outlook
area as supercells or small bows from later this morning into
afternoon, with weak but sufficient low-level instability to support
a marginal damaging-wind/tornado threat.

This will occur as increasing large-scale DCVA/cooling aloft and
mass response to low-level cyclogenesis result in strengthening of
both lift and destabilization, atop the favorable sea-air
thermodynamic fluxes near the Gulf Stream.  Meanwhile the relatively
well-modified Atlantic maritime/tropical layer south of the marine
front will struggle to reach very far inland today prior to cold-
frontal passage, amidst considerable cloud cover and precip that
reinforces inland static stability.  Nonetheless, surface dew points
in the 60s F will support surface-based effective-inflow parcels in
parts of the coastal areas and Outer Banks, offsetting weak midlevel
lapse rates enough to 300-800 J/kg MLCAPE.  Veering winds with
height in low levels will support locally favorable low-level shear,
though deep shear will be modest (effective-shear magnitudes
increasing to 35-40 kt just ahead of the cold front).

...FL...
Widely scattered to scattered thunderstorms are expected this
afternoon along a hybrid prefrontal wind-shift, convergence and
sea-breeze boundary.  The most intense cells may produce strong/
isolated severe gusts and hail.

Destabilization through much of the troposphere is expected today
as:
1.  The southern rim of large-scale DCVA/cooling aloft brushes the
area from a southern-stream perturbation, and
2.  Diurnal heating of a favorably moist boundary layer boosts
low-level lapse rates and removes MLCINH.
Modified RAOBs and forecast soundings suggest this should lead to
around 2000-2500 J/kg MLCAPE atop a shallow but well-mixed boundary
layer.  Though winds along and east of the boundary will veer with
height, modest speeds in low/middle levels will keep vertical shear
weak.  Multicellular activity with strong/damaging wet downbursts
appears to be the most probable source of severe potential today.

..Edwards/Smith.. 04/18/2022