SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0258 PM CDT Fri Sep 08 2023
Valid 082000Z - 091200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE NORTHEAST AND MID-ATLANTIC REGION...AND OVER PARTS OF THE
EASTERN TEXAS/SOUTHERN LOUISIANA VICINITY...
...SUMMARY...
Scattered damaging winds and isolated large hail remain possible
across parts of the Mid-Atlantic States into New England into this
evening, and across parts of the South-Central States in multiple
rounds through tonight.
...Discussion...
Convection, and associated severe-weather risk, continues to evolve
largely as anticipated in earlier outlooks. As such, no substantive
changes to outlook areas or reasoning appear necessary at this time.
The most substantial adjustments were to remove portions of Florida
from MRGL risk, in the wake of earlier storms which have moved
offshore, and to trim parts of the MRGL and SLGT north of the
convective line now moving southward across southern Louisiana.
..Goss.. 09/08/2023
.PREV DISCUSSION... /ISSUED 1123 AM CDT Fri Sep 08 2023/
...Mid-Atlantic States to New England...
Thunderstorms this afternoon through early evening will again be
capable of damaging winds and hail, in a scenario somewhat similar
to yesterday. Late morning/midday observations continue to suggest
that abundant insolation east of the Appalachians, combined with a
pervasive plume of 60s to low 70s F surface dew points, will yield a
pronounced west/east-oriented gradient in MLCAPE across the region,
with peak values approaching 2500-3000 J/kg over the coastal plain.
Scattered thunderstorms are expected to develop within the MLCAPE
gradient from near the West Virginia/Virginia border northeast into
parts of eastern New England. With forecast soundings suggesting
nearly unidirectional southwest flow will weaken with height from
the mid to upper-levels, multicell clustering will dominate. 700-mb
winds in excess of 30 kt from eastern New York to Maine should
support slightly more organized clustering. Steeper low-level lapse
rates from Virginia to the Delaware Valley should compensate for the
weaker flow and support relatively more prolific downburst
potential. Scattered damaging winds along with isolated severe hail
are expected regionally, mainly from mid-afternoon into evening.
...Texas/Oklahoma Red River vicinity and Sabine Valley...
An elevated semi-organized linear cluster of storms persists
southward at late morning across northern Louisiana. While boundary
layer inhibition still currently exists, relatively cloud-free skies
are noted to its south, with some potential that this cluster and/or
new development on its western-peripheral outflow could root within
a very moist/heating boundary layer. If so, damaging winds would be
possible across southern Louisiana/southeast Texas.
Farther to the northwest along the Red River Valley, record hot
temperatures and a deep-mixed boundary layer should support sporadic
downbursts from late afternoon to early evening with isolated
thunderstorms that develop near the surface front. Some of this
activity may try to congeal and grow upscale south-southeastward
into east Texas during the evening/overnight within the persistent
northwest flow regime atop the low-level moisture gradient. But low
confidence exists in this scenario, with potential effects of the
daytime round of storms modulating the downstream environment and
ascent.
...Northern High Plains to Black Hills vicinity...
Relatively isolated instances of severe wind and hail will be
possible across the region. A low-amplitude shortwave impulse along
the international border over the northern Rockies will move
eastward today toward the northern High Plains. Forcing for ascent
attendant to this wave will support isolated to scattered
thunderstorms focused primarily across the southern half of Montana,
but perhaps also far northeast Wyoming and the Black Hills vicinity
as well. While there will be MLCIN concerns to the north and east,
35-45 kt effective bulk shear should support a few organized cells
capable of isolated severe wind and hail. A more favorable supercell
wind profile will conditionally exist near the Black Hills pending
sustained storm development.
...Northern/central Florida...
A mid-level low near the Florida/Georgia border should slowly weaken
as it drifts south today. Relatively cold mid-level temperatures
sampled by the 12Z JAX sounding of -13 C at 500 mb should support
enhanced CAPE profiles between 700-300 mb yielding pronounced
vertical growth. Effective bulk shear will tend to remain weak,
especially near the cold core, suggesting the potential for
organized storms is limited. Still, sporadic occurrences of
marginally severe hail and wind are possible, mainly this afternoon.
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