SPC AC 121715
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1115 AM CST Tue Nov 12 2024
Valid 131200Z - 141200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE LOWER
MISSISSIPPI VALLEY/CENTRAL GULF COAST REGION...AND COASTAL PORTIONS
OF PACIFIC NORTHWEST...
...SUMMARY...
A marginal tornado/wind threat is apparent on Wednesday afternoon
into Wednesday night across a part of the central Gulf Coast States.
Thunderstorms with strong to locally severe gusts are also possible
near the immediate coasts of Washington, Oregon, and northern
California.
...Synopsis...
A shortwave trough is forecast to move from the Plains through the
MS Valley on Wednesday, becoming more negatively tilted as it does.
An occluded surface low associated with this system will begin the
period over the mid MO Valley before moving eastward across IA and
reaching the northern IL early Thursday morning. More consequently
for the severe-weather potential, a secondary triple-point low is
expected to progress eastward across the northern portion of the
Southeast states, along the northern edge of an eastward-evolving
warm sector. Cold front associated with this low will gradually move
eastward across the Southeast states during the day.
Farther west, an upper-level trough is forecast to progress farther
inland across the western CONUS, as an embedded shortwave trough
moves across northern CA into the interior Northwest/northern Great
Basin.
...Lower Mississippi Valley/Central Gulf Coast...
General expectation is for a triple-point surface low to evolve over
the Mid-South vicinity through the early afternoon as low-level
moisture continues to advect northward across the central Gulf Coast
region. Dewpoints in the upper 60s/low 70s are anticipated ahead of
this low and associated cold front. The airmass is expected to
destabilize amid this low-level moisture, but overall buoyancy will
still be modest given the lack of steep lapse rates. The combination
of destabilization and increasing ascent is forecast to result in
thunderstorm development across the warm sector, but along and ahead
of the eastward-progressing cold front.
The stronger shear will likely be displaced north of the stronger
buoyancy, but enough shear is expected across the warm sector to
support organized storms if updrafts can persist and deepen. This
evolution could support a few marginal supercells and/or stronger
clusters during the afternoon and evening, with a threat of locally
damaging winds and possibly a tornado or two.
Elevated storms will also be possible through the day/evening to the
north of the richer surface moisture. While effective shear will be
sufficient for a few strong elevated storms, the severe potential
with northward extent will tend to be limited by weak midlevel lapse
rates and generally marginal buoyancy.
...WA/OR/Northern CA coasts...
Cold mid-level temperatures (i.e. -24 to -28 deg C at 500 mb)
associated with the upper trough are expected to spread eastward
throughout the day. These cold mid-level temperatures and associated
steep mid-level lapse rates will contribute to modest buoyancy along
the coastal portions of the Pacific Northwest. Highest storm
coverage is anticipated over the northern CA coast vicinity from the
late morning into the early afternoon along as the frontal band
moves through, but persistent forcing for ascent within this
modestly buoyant airmass is expected to result in more cellular
storms throughout the remainder of the afternoon and evening. A more
linear mode is anticipated within the frontal band, with a few
convectively enhanced gusts possible. Low-topped cellular activity
is anticipated in the wake of the frontal band, with a few instances
of small hail, and potentially even a brief tornado, possible.
..Mosier.. 11/12/2024
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