Source: US National Oceanic and Atmospheric Administration
SPC AC 250556
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1256 AM CDT Sat Jul 25 2026
Valid 251200Z – 261200Z
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF
CENTRAL MT…AND ALSO ACROSS PARTS OF SD…
…SUMMARY…
Storms with scattered severe wind gusts are possible across parts of
Montana and South Dakota this afternoon and evening.
…MT into SD and vicinity…
An expansive upper ridge will remain anchored over much of the
southwest and central CONUS through the period. Very hot
temperatures are expected this afternoon from MT into the Dakotas.
Isolated to scattered storms within the hot and well-mixed
environment will result in a broad area of at least isolated
severe-wind potential. 5% wind probabilities have been expanded to
cover this potential, with 15% wind probabilities (equivalent to
categorical Level 2/Slight Risk) added across parts of MT and SD,
where terrain features may enhance storm coverage within the
favorable severe-wind environment.
For parts of western/central MT, convection that develops by
early/mid afternoon near the high terrain is expected to spread
eastward into the hot and well-mixed environment. This convection
may be aided by a low-amplitude midlevel vorticity maximum moving
around the periphery of the upper ridge. Increasing storm coverage
and gradually strengthening mid/upper-level flow may allow for one
or more outflow-driven clusters to develop and spread
east-northeastward into early evening, with a threat of severe
gusts. Localized gusts of 75+ mph cannot be ruled out, especially if
deeper convection is able to spread into areas where very deep
mixing and heating to near/above 100 F occurs prior to storm
arrival.
Farther east, very strong heating is expected across parts of
western/central SD, with temperatures in some areas potentially
rising to near/above 105 F. Low-level moisture will be relatively
sparse, but MLCAPE of near/above 1000 J/kg will be possible where
50s F dewpoints can be maintained within the well-mixed environment.
Initial storm development near the Black Hills will quickly become
outflow dominant as it spreads eastward, with an increasing threat
of severe gusts. Deep-layer shear will be somewhat favorable for
organized convection, and some guidance depicts development of a
persistent cluster or loosely organized MCS that moves eastward
across SD along a weak surface boundary. Should this occur, a
corridor of more organized severe-wind threat (with gusts
potentially near/above 75 mph) will be possible.
…Northern/eastern MN into WI and Upper MI…
Conditional severe potential remains evident across parts of the
Upper Midwest, though confidence regarding storm coverage and timing
remains very low within the weakly forced environment. Moderate to
strong destabilization is possible along/south of a surface front
that is forecast to extend from northeast ND into northern MN/WI by
late afternoon. Effective shear of 50+ kt will be more than
sufficient for storm organization, but most guidance remains rather
muted regarding potential for diurnal storm development. If storms
are able to develop during the afternoon or evening, then a threat
for hail, damaging wind, and possibly a tornado could evolve. Even
if diurnal storm development is limited, vigorous elevated storms
may evolve within a warm-advection regime near/north of the front
late tonight, which would pose a threat for hail and perhaps locally
damaging wind. Confidence remains too low to include more than
Level-1/Marginal Risk equivalent probabilities at this time.
…Northeast NV/northern UT into eastern ID…
Storm development is expected during the afternoon across parts of
northeast NV, along the western periphery of the upper ridge. These
storms will spread into adjacent parts of southeast ID and northwest
UT with time. Strong to locally severe gusts will be possible with
these storms as they move northeastward through a well-mixed
environment.
…South-central/southeast AZ…
High-based convection is again expected across southeast AZ during
the afternoon, with initial downburst potential. Modest enhancement
to easterly flow along the southern periphery of the upper ridge may
allow for localized strong to severe gusts to spread westward into
parts of south-central AZ, before convection weakens later Saturday
night.
..Dean/Squitieri.. 07/25/2026
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