LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0742 AM CDT Fri Sep 08 2023
Valid 081300Z - 091200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS MID-ATLANTIC TO
NEW ENGLAND AND PARTS OF THE SOUTH-CENTRAL STATES...
...SUMMARY...
Scattered damaging winds and isolated large hail will be possible
across parts of the Mid-Atlantic States into New England from
mid-afternoon into this evening, and across parts of the
South-Central States in multiple rounds through tonight.
...Mid-Atlantic States to New England...
Abundant insolation east of the Appalachians combined with a
pervasive plume of 60s to low 70s 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 WV/VA border northeast into parts of western
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 kts should be confined from eastern NY to ME should
support slightly more organized clustering. Steeper low-level lapse
rates from VA to the DE Valley should compensate for the weaker flow
and support relatively more prolific downburst potential. In
aggregate, scattered damaging winds along with isolated severe hail
are expected, mainly from mid-afternoon into the evening.
...Red River and the Sabine Valleys...
Elevated convection has persisted for the past several hours in the
Ozarks vicinity. During the past few hours, storm-scale
consolidation has yielded small cluster growth across western AR.
How this activity evolves through late morning into the afternoon is
still uncertain. Increasingly negative low-level theta-e advection
may be sufficient to decay convection, a signal consistently
pronounced within HRRR runs prior to 11Z. Meanwhile, multiple other
00Z HREF members and earlier RRFS runs suggest convection will not
weaken and should actually intensify as downstream diurnal heating
ensues on a plume of PW values from 1.7-1.9 inches. The 11Z HRRR and
10Z RRFS have trended towards somewhat greater consistency with the
06Z NAM-Nest in suggesting that outflow from this morning's activity
will be the main impetus for downstream development across western
LA into far southeast TX this afternoon. Scattered damaging winds
and isolated large hail will be the main threats.
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 near the surface front. Some of this activity may try
to congeal and grow upscale south-southeast in east TX during the
evening into tonight 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...
A low-amplitude shortwave impulse along the international border
over the northern Rockies will move east today. Ascent attendant to
this wave will support isolated to scattered thunderstorms focused
primarily across southern MT. 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 should exist near the Black Hills,
but pronounced MLCIN may inhibit sustained storm development.
...North to central FL...
A mid-level low near the FL/GA 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.
..Grams/Mosier.. 09/08/2023
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