142
ACUS03 KWNS 200736
SWODY3
SPC AC 200735

Day 3 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
0235 AM CDT Sun Jul 20 2025

Valid 221200Z - 231200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TUESDAY INTO
TUESDAY NIGHT ACROSS PARTS OF WESTERN UPPER MICHIGAN...NORTHWESTERN
WISCONSIN...MINNESOTA...SOUTHEASTERN NORTH DAKOTA...SOUTH
DAKOTA...MUCH OF NEBRASKA AND PARTS OF SOUTHEASTERN
MONTANA...NORTHEASTERN WYOMING AND NORTHEASTERN COLORADO...

CORRECTED A POINT ON THE CATEGORICAL THUNDER LINE OVER THE LAKE
HURON VICINITY

...SUMMARY...
Scattered strong thunderstorm development may impact parts of the
northern Great Plains into the Upper Midwest Tuesday into Tuesday
night, and pose at least some risk for severe wind and hail.

...Discussion...
Models indicate that a center of higher mid-level heights may become
increasingly prominent across the middle Mississippi/lower Ohio
Valley region during this period, within persistent ridging
encompassing much of the interior U.S.  Modest, anticyclonic flow
around the northern periphery of this feature is likely to be
maintained across the northern Great Basin, Rockies and Great Plains
through the Great Lakes and adjacent portions of Ontario and Quebec.
 It appears that ridging will also remain prominent across much of
the northeastern Pacific, though it may begin to undergo some
suppression.

Weak mid-level troughing is likely to linger between the ridging
across the Pacific coast vicinity, with one embedded short wave
impulse forecast to accelerate northeast of the mountains of western
Montana.  It appears that this will trail a significant mid-level
low continuing to slowly migrate east of the Canadian Northwest
Territories toward Hudson Bay, but there is spread among the various
models concerning this.

The stronger perturbation will be accompanied by a modest surface
cyclone, with a trailing cold front forecast to advance across the
international border into the northern Great Plains late Tuesday
into Tuesday night.

...Northern Great Plains into Upper Midwest...
Beneath the mid-level ridging, insolation within a seasonably moist
boundary-layer appears likely to once again contribute to moderate
to large potential instability across parts of the middle Missouri
Valley and adjacent Great Plains, within modestly deep pre-frontal
surface troughing.  This low-level moisture is forecast to advect
northeastward toward the Upper Midwest late Tuesday through Tuesday
night, beneath thermodynamic profiles characterized by generally
steep lapse rates, but with warm, capping layers aloft.

Near the southern periphery of a belt of strengthening southwesterly
mid-level flow, the environment is likely to become at least
conditionally supportive of organized thunderstorm development,
including supercells and upscale growing clusters.  However, south
of the international border, forcing for ascent to support
thunderstorm development is likely to mostly be linked to subtle
perturbations progressing around the northern periphery of the
mid-level ridging, which remain uncertain at this time.

There does appear a general consensus for increasing thunderstorm
development across parts of Minnesota into Wisconsin, particularly
Tuesday night.  But this may be largely rooted in
lower/mid-tropospheric warm advection, above a stable
boundary-layer, and within relatively warm thermodynamic profiles,
where the extent of the potential for severe wind and hail is still
unclear.

..Kerr.. 07/20/2025

$$