ACUS02 KWNS 130444
SWODY2
SPC AC 130442

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1142 PM CDT Sat Sep 12 2026

Valid 141200Z - 151200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE MONDAY
AFTERNOON INTO EVENING ACROSS PARTS OF EASTERN NEBRASKA INTO WESTERN
AND CENTRAL IOWA...

...SUMMARY...
An isolated severe thunderstorm or two, and perhaps a small
organizing cluster of storms, may impact parts of eastern Nebraska
into western Iowa late Monday afternoon into early evening.

...Discussion...
Latest model output remains generally unchanged from prior runs
concerning the large-scale pattern evolution through this period. 
To the east of a still fairly prominent mid-level high slowly
beginning to shift eastward across the northeastern Pacific, a
number of short wave perturbations are forecast to dig through
multiple branches of westerlies across the Pacific coast and higher
latitudes of northwestern North America into the Canadian Prairies.

As this occurs, and downstream mid/upper ridging becomes
increasingly prominent across the southern Great Plains through
lower Great Lakes and north Mid Atlantic Seaboard, a notable remnant
mid-level cyclonic circulation is forecast to accelerate more
rapidly east-northeast of the northern U.S. Rockies, across the
international border into northwestern Ontario by late Monday night.
 It appears that this will be accompanied by fairly significant
surface cyclogenesis, and considerable strengthening of south to
southwesterly lower/mid-tropospheric wind fields across much of the
northern U.S. Great Plains through Upper Midwest/Great Lakes region.

While an associated increase in vertical shear will contribute to an
environment conditionally supportive of organized severe weather
potential, destabilization within the evolving warm sector remains
much more uncertain.  Fairly widespread weak, elevated convection
may overspread much of the northern Great Plains and middle to lower
Missouri through Upper Midwest and adjacent Great Lakes region,
reinforcing a relatively cool/stable boundary-layer to the north of
a stalled surface frontal zone across the lower Missouri Valley
through central Great Plains, before it begins to retreat northward.

...Southern Mid Missouri Valley into central Great Plains...
There does appear a general consensus within/among the model output
that the northward retreating low-level baroclinic zone may reach
the southern fringe of the westerlies, across parts of Nebraska
through Iowa by late Monday afternoon.  It appears possible that
boundary-layer moistening will contribute to a corridor of
destabilization supportive of scattered vigorous thunderstorm
development through the late afternoon and evening.

Particularly where the southern periphery of a strong southerly
low-level jet impinges on this front, across the eastern Nebraska
into western Iowa vicinity, at least some guidance continues to
suggest a scenario where the environment could become supportive of
the evolution of an isolated intense supercell into small upscale
growing cluster for a period late Monday afternoon into evening.

..Kerr.. 09/13/2026

$$
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