688
ACUS01 KWNS 051954
SWODY1
SPC AC 051952

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0252 PM CDT Fri Sep 05 2025

Valid 052000Z - 061200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF THE
TENNESSEE VALLEY AND UPPER OHIO VALLEY...

...SUMMARY...
Scattered damaging winds, isolated severe hail, and a brief tornado
or two are possible from the Upper Ohio to Tennessee Valleys, mainly
late this afternoon and evening.

...20z Update...
The previous forecast remains on track with no changes required. As
of 1930 UTC, GOES imagery shows meager vertical development of the
cumulus field along and ahead of the cold front across KY and TN.
However, weak surface pressure falls are noted along the frontal
zone, hinting that ascent may be gradually increasing. This trend
should continue as ascent associated with a subtle shortwave trough
over southeast MO continues to spread east, and should aid in
thunderstorm development by late afternoon/early evening. These
observed trends, along with trends in recent CAM guidance, align
with the ongoing forecast.

Across north TX, convective initiation appears more imminent and
should result in increasing severe hail/wind potential through the
evening hours. Based on recent mesoanalysis and forecast soundings,
the convective environment remains adequate for a few strong to
severe thunderstorms. See the previous discussion for additional
details.

..Moore.. 09/05/2025

.PREV DISCUSSION... /ISSUED 1130 AM CDT Fri Sep 05 2025/

...Ohio Valley/Central Appalachians to the Tennessee Valley...
A large-scale upper trough/low will remain centered over Ontario
today, with mid/upper-level troughing extending southward across
much of the Great Lakes/Midwest into the OH Valley. A cold front
will continue to advance slowly southeastward across portions of the
Mid-South and OH Valley through this evening. Daytime heating of a
seasonably moist low-level airmass ahead of this front over the TN
Valley will likely yield upwards of 1500-2500 J/kg MLCAPE by late
afternoon, mainly in KY/TN. Weaker instability is forecast with
northward extent into the upper OH Valley and central Appalachians.

Forcing for ascent aloft will remain nebulous for much of the day,
with generally neutral mid-level heights and stronger flow remaining
confined to the north of the surface cold front. Still, a subtle
mid-level perturbation over eastern KS and the Ozarks late this
morning should continue eastward towards the Mid-South and lower OH
Valley by late afternoon/early evening. This feature, along with
modest low-level convergence along the front, may be sufficient to
encourage initial convective development by 21-23Z across parts of
KY/TN. Even with stronger flow aloft remaining displaced to the
north of the surface warm sector, some veering and gradual
strengthening with height through mid/upper levels should support
sufficient deep-layer shear for updraft organization.

Current expectations are for multiple clusters to develop and pose a
risk for mainly severe/damaging winds as they spread eastward across
the TN and upper OH Valleys through the late afternoon and evening.
With cool temperatures aloft and marginal deep-layer shear to
support supercells, some of this activity could also pose a threat
for isolated hail, especially any cells that can remain at least
semi-discrete. A brief tornado or two also appears possible,
although low-level shear should remain fairly limited given
veered/west-southwesterly low-level flow. With a relatively narrow
warm sector expected, convection should generally weaken this
evening as it moves into the higher terrain of the central
Appalachians and encounters a less unstable airmass.

...Mid-South to North Texas...
An elongated mid-level thermal trough, characterized by 500 mb
temperatures around -8 to -12 C per RAP analysis and 12Z OUN/FWD
observed soundings, extends into much of OK and north TX, well to
the south of the vertically stacked cyclone over Ontario. Low to
mid-level flow should remain modest across this region, with some
signal from various NAM/RAP forecast soundings of a veer-back-veer
signature. Strong speed shear should remain confined above 500 mb,
coincident with poor upper-level lapse rates atop steeper mid-level
lapse rates. This suggests a messy convective mode should be common
as convection increases in the late afternoon and evening, along the
more west/east-oriented portion of the surface cold front. Have
maintained the Marginal Risk for an isolated severe hail/wind threat
with a small westward expansion with this update.

...Oregon...
Isolated to scattered thunderstorms should develop today across
parts of OR as a weak mid-level trough moves northward across the
Pacific Northwest Coast. While low/mid-level flow is expected to
remain rather modest, steepened low-level lapse rates could support
isolated strong/gusty winds with any high-based convection that
develops this afternoon/evening.

$$