Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1106 AM CDT Fri Jul 18 2025
Valid 181630Z - 191200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
VIRGINIA AND NORTH CAROLINA...AND WESTERN PARTS OF THE MIDWEST...
...SUMMARY...
Scattered severe thunderstorms with large hail, damaging winds, and
a couple of 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...
Late morning surface analysis places a stationary front draped from
west to east from the mid MS Valley eastward into the Mid-Atlantic
states. Visible satellite/radar mosaic imagery shows a couple of
weak MCVs moving east over the northern VA/MD vicinity and over far
eastern KY. The latter disturbance will probably prove instrumental
in aiding storm development across VA into northern NC this
afternoon.
South of the front, rich low-level moisture and heating will act to
offset weak mid-level lapse rates and yield moderate to strong
buoyancy from southeast MO eastward to the Mid-Atlantic coast.
Early indications of a swelling cumulus field over the WV/VA
mountains will gradually evolve into a cluster of storms as
convective inhibition continues to erode through early afternoon.
Other clusters of storms will develop and move west to east given
marginal deep-layer mean westerly flow. Although small hail
0.50-1.00 inch in diameter is possible with the strongest cores, the
primary hazard with the stronger storms will be damaging gusts
(50-65 mph) with the more intense water-loaded downdrafts. This
activity will likely diminish by the early to mid evening.
...South Dakota/Nebraska into Minnesota/Iowa...
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. An initially appreciable capping inversion will
inhibit surface-based storm development until heating gradually
weakens inhibition by late afternoon. A very unstable airmass is
forecast by late afternoon/early evening, but nebulous forcing lends
uncertainty in terms of storm development/timing. Models suggest
storms will primarily develop this evening associated with
strengthening low-level theta-e advection. Supercells are possible
early in the convective life cycle with a risk for all hazards,
including the possibility for a couple of tornadoes, but large hail
may be the main hazard. Upscale growth into a cluster or MCS is
possible near the terminus of a southwesterly 850-mb LLJ with severe
gusts the becoming the primary threat. Models vary considerably
whether storm intensity is maintained through much of the overnight
and beyond the Day-1 period, or if a gradual diminishing in severe
occurs.
...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. Steep low/mid-level lapse rates and a deep, very well-mixed
boundary layer should support isolated severe gusts with the
stronger thunderstorms. 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.
..Smith/Weinman.. 07/18/2025
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