ACUS01 KWNS 181244
SWODY1
SPC AC 181243

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0743 AM CDT Fri Jul 18 2025

Valid 181300Z - 191200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
VIRGINIA/NORTH CAROLINA...AND PARTS OF CENTRAL/EASTERN
NEBRASKA...SOUTHEAST SOUTH DAKOTA...SOUTHWEST MINNESOTA...AND
WESTERN/CENTRAL IOWA...

...SUMMARY...
Scattered severe thunderstorms with large hail, damaging winds, and
a few tornadoes are possible across parts of the Corn Belt in Iowa,
Minnesota, Nebraska, and South Dakota this evening into tonight.
Scattered damaging winds are possible across parts of Virginia and
North Carolina this afternoon.

...Virginia/North Carolina to the Mid-South...
A generally west-east oriented quasi-stationary front reinforced by
outflow from earlier convection should serve as a low-level forcing
mechanism for thunderstorm development this afternoon from parts of
VA/NC westward to the Mid-South and vicinity. A seasonably moist
airmass will be present today along/south of this front, with
surface dewpoints generally ranging from the upper 60s in higher
elevations to mid 70s elsewhere. Even though mid-level lapse rates
are expected to remain rather modest, ample daytime heating of the
moist low-level airmass will contribute to sizable MLCAPE by early
to mid afternoon. With a subtropical anticyclone centered off the
Southeast Atlantic Coast and stronger flow aloft associated with
various mid-level perturbations expected to remain over the Great
Lakes/Northeast, large-scale ascent in the vicinity of the surface
front will be nebulous at best.

Regardless, scattered to numerous thunderstorms should develop
along/near this boundary through the afternoon, while spreading
generally eastward this evening. With modest mid-level westerly flow
forecast, deep-layer shear appears marginal for thunderstorm
organization. The greatest threat for scattered damaging winds
should focus across parts of VA/NC this afternoon and early evening,
where semi-organized clusters and short line segments appear
possible given slightly stronger deep-layer shear. Otherwise,
isolated damaging winds may occur even with less organized
convection farther west towards parts of the TN Valley/Mid-South, as
steepened low-level lapse rates potentially support microbursts.
There does appear to be a gap in scattered convective coverage
across parts of MO and vicinity, where the Marginal Risk has been
removed with this update.

...South Dakota/Nebraska into Minnesota/Iowa...
Elevated convection across parts of SD may continue to pose an
isolated hail threat this morning, before it eventually weakens with
the gradual lessening of a southerly low-level jet. A belt of strong
westerly mid-level flow will remain in place over the northern tier
of the CONUS from MT eastward towards the Great Lakes. Gradual
low-level moistening is forecast through this evening ahead of a
weak front forecast to be in place over the eastern Dakotas into
western NE. Diurnal heating and modestly steepened mid-level lapse
rates will contribute to moderate to strong MLCAPE across parts of
NE/southeast SD into IA. But, nebulous forcing for ascent and
residual capping should tend to suppress surface-based convective
development across these areas for much of the day. Occasional
severe hail may occur with mainly elevated convection to the north
of the front in MN.

A gradually strengthening southerly low-level jet this evening
(mainly after 00Z) should aid in convective initiation along/near
the front from central/northeast NE into southeast SD/southwest MN.
Various NAM/RAP forecast soundings across this region suggest ample
instability and strong deep-layer shear will be present to support
supercells with attendant large hail threat initially. Low-level
shear should also be strong enough for a tornado threat with these
supercells, although there may be a fairly narrow spatial/temporal
window for convection to remain discrete this evening. Upscale
growth into a bowing cluster should occur through mid to late
evening, with a threat for mainly scattered severe/damaging winds as
this convection tracks into parts of IA overnight, before eventually
weakening early Saturday morning.

...Great Basin into Wyoming and Far Southern Montana...
Initially high-based convection should develop this afternoon across
parts of the Great Basin into WY as modest ascent associated with a
weak/low-amplitude mid-level impulse spreads eastward across these
areas. While low-level moisture and deep-layer shear will remain
limited, steepened low/mid-level lapse rates amid a very well-mixed
boundary layer should support isolated severe gusts with any
thunderstorms that can be sustained amid weak instability. Somewhat
greater low-level moisture should be present this afternoon across
parts of southern MT into northern/eastern WY, generally along/east
of the Bighorn/Laramie Mountains. Isolated severe hail may occur
with marginal supercells given greater instability/shear forecast
across these areas.

..Gleason/Bentley.. 07/18/2025

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