Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1234 AM CDT Wed Aug 20 2025
Valid 201200Z - 211200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TODAY ACROSS THE
WESTERN AND CENTRAL GULF COAST STATES AND THE INTERNATIONAL BORDER
VICINITY OF NORTH DAKOTA...
...SUMMARY...
Scattered thunderstorms developing this afternoon and evening across
the western and central Gulf Coast states may pose a risk for
localized potentially damaging wind gusts. Otherwise, there appears
some risk for an isolated severe thunderstorm or two across parts of
northern North Dakota.
...Discussion...
Models indicate that a prominent mid/upper high will be maintained
over the Four Corners vicinity through this period. However,
initially amplified ridging extending to its north, as far as the
Canadian Prairies, appears likely to become suppressed southeastward
toward the central international border vicinity, as a significant
short wave perturbation progresses east of the Canadian Rockies into
Prairies by late tonight. It appears that this may be accompanied
by weak cyclogenesis across southern Saskatchewan toward the central
Saskatchewan/Manitoba border vicinity, with a trailing cold front
advancing across the Montana international border by late tonight.
At the same time, an increasingly sheared perturbation will continue
progressing through weak larger-scale mid-level troughing digging
across the Northeast, and southeastward around the periphery of the
high, across the Ohio/Tennessee Valleys and southern Great Plains.
To the southeast of this feature, Hurricane Erin is forecast to turn
slowly north-northeastward, offshore of the southern through middle
Atlantic Seaboard.
...Gulf Coast States...
A diffuse surface frontal zone, reinforced in segments by convective
outflow, will continue slowly southward ahead of the mid-level shear
axis, likely reaching portions of central Texas through Louisiana
and central/northern Mississippi and Alabama by mid to late
afternoon. Along and ahead of this front, a corridor of stronger
heating of a seasonably moist boundary layer, perhaps still
coincident with a residual plume of relatively steep
lower/mid-tropospheric lapse rates, may continue to contribute to
thermodynamic profiles supportive of localized downbursts and gusty
winds on convectively generated surface cold pools. It is not clear
that the severe threat will be any more widespread than the sparse
coverage of preceding days, but it may perhaps be marginally
sufficient to justify 5 percent severe wind probabilities.
...North Dakota...
Models indicate that a narrow corridor of moderate to large
potential instability may develop along/ahead of the surface cold
front, a pre-frontal surface trough and developing warm frontal zone
across parts of the Dakotas into eastern Saskatchewan by late this
afternoon. However, beneath the nose of a plume of warm and capping
elevated mixed-layer air, mid/upper support for the initiation of
boundary-layer based thunderstorm development is forecast to
generally remain to the north of the international border.
While the risk for severe thunderstorms appears largely conditional,
guidance does indicate that a weak surface low may develop within
the pre-frontal troughing and provide a potential focus for
convective development across northwestern North Dakota late this
afternoon and evening. If this forcing, coupled with the approach
of convective temperatures, is sufficient to overcome the mid-level
inhibition, forecast soundings indicate the environment will be
conducive to supercell development.
..Kerr/Lyons.. 08/20/2025
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