ACUS01 KWNS 182002
SWODY1
SPC AC 182000
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0200 PM CST Tue Nov 18 2025
Valid 182000Z - 191200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE LOWER OHIO VALLEY AND MIDDLE MISSISSIPPI VALLEY...
...SUMMARY...
Widely scattered severe storms are possible across parts of the
middle Mississippi Valley and lower Ohio Valley this afternoon and
evening.
...20Z Update...
The primary change with this update was the addition of a Slight
Risk (2/5) over parts of the Lower OH Valley and Mid MS Valley --
driven by 15-percent hail probabilities. The latest visible
satellite imagery shows an increasingly agitated boundary-layer
cumulus field evolving across southeast MO -- in the vicinity of a
frontal wave/weak surface low. Continued heating amid increasing
boundary-layer moisture ahead of this feature should erode
inhibition through the remainder of the afternoon and support
isolated to widely scattered thunderstorms along a pre-frontal
surface trough. Any storms that form will be moving into an
environment characterized by around 50 kt of effective shear and
weak-moderate surface-based buoyancy. This will conditionally favor discrete/semi-discrete supercells capable of producing large hail
and locally strong gusts. While less certain, a couple of tornadoes
cannot be ruled out if established supercells evolve, given
sufficient low-level hodograph curvature. Elsewhere, the Marginal
Risk was expanded slightly northward to account for an ongoing
elevated hail risk.
..Weinman.. 11/18/2025
.PREV DISCUSSION... /ISSUED 1030 AM CST Tue Nov 18 2025/
...Middle Mississippi Valley/Lower Ohio Valley...
Clusters and northeast/southwest-oriented bands of elevated
thunderstorms persist at late morning either side of the Ohio River,
spanning southeast Indiana into northern/western Kentucky including
near the confluence of the Ohio and Mississippi Rivers. This
convection will result in some additional net south/southwestward
forecast focus of the warm sector later today, even while fairly
aggressive warm-sector moistening is occurring across the Ozarks as
surface dewpoints climb through the lower/some middle 60s F.
A shortwave trough/moderately strong jetlet over Iowa and northern
Missouri this morning will continue to gradually minor/open while
moving east-southeastward toward the middle Ohio Valley by tonight.
Given the trend of this system, the related surface low will
gradually weaken while air mass modification/convective recovery
occurs with a northeastward-expanding warm sector toward the lower
Ohio Valley.
Current expectations are for some re-intensification of convection
to occur this afternoon across far southeast Missouri, southern
Illinois and western Kentucky, although some of these developmental/environmental details depend on the disposition of still-recurring convection near/south of the Ohio River. There is
still some sub-regional uncertainty with how far north the surface
warm sector will be able to advance, and daytime heating may be
muted by persistent cloudiness. But, the best combination of weak to
locally moderate instability and favorable deep-layer shear will
generally overlap across the aforementioned region this afternoon
and evening as a 50-60+ kt westerly mid-level jet moves overhead.
Any sustained supercell may be capable of producing severe hail
along with locally damaging winds, with elevated convection possible
north of the warm front into south-central Illinois/southern
Indiana. Some threat for a tornado or two may also exist if
sufficient boundary-layer instability can advance far enough
northward in tandem with the warm front and enhanced low-level shear
to support surface-based thunderstorms.
A narrow zone centered on far southeast Missouri, far southern
Illinois, western Kentucky and northwest Tennessee will continue to
be closely monitored and reevaluated for an upgrade (20z D1 update)
should confidence in surface-based storms increase near the surface
low/warm front late this afternoon and early evening.
...Lower Colorado River Valley/Arizona...
A closed mid/upper-level low along the coast of central/southern
California will make only slow progress southward today. Large-scale
ascent associated with a south-southwesterly mid-level jet should
encourage additional convective development today across parts of
the lower Colorado River Valley and Arizona. While deep-layer shear
appears adequate for organized updrafts, weak instability will
likely limit the overall severe threat across this region, although
small hail/gusty winds a few stronger storms could occur this
afternoon.
$$
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