Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1233 AM CDT Fri Sep 12 2025
Valid 121200Z - 131200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM EASTERN
MONTANA INTO THE DAKOTAS AND ACROSS THE FOUR CORNERS REGION...
...SUMMARY...
A few storms capable of isolated severe wind gusts are possible
across the Four Corners region, and from eastern Montana into the
Dakotas.
...Synopsis...
An upper trough will remain over the Intermountain West, making slow
eastward progress through the period. An upper disturbance is
forecast to move from CO into the Dakotas late in the day, while a
strong midlevel jet rounds the base of the trough across AZ
overnight. Gradual height falls will occur across the length of High
Plains primary overnight as the Plains upper ridge gradually
weakens.
At the surface, a weak area of low pressure is forecast over SD,
with a trough extending westward across WY and into the Great Basin
during the afternoon with strong heating. Dewpoints in the 60s F
will be common across the mid MO Valley, especially from MN into the
Dakotas where surface winds will be backed north of the low. Rather
veered/southwesterly 850 mb flow is forecast overnight, with only
pockets of positive theta-e advection.
...Eastern MT into the Dakotas...
Moderate instability will develop over much of the northern Plains,
but beneath temporary upper ridging. Storms are most likely to form
over eastern MT and WY, beneath cooler temperatures aloft and where
less capping will exist. Isolated hail may occur with these widely
scattered afternoon cells. Later in the evening, a few cells may
persist into the western Dakotas with hail potential, and there
appears to be a possibility of scattered damaging gusts as
activity/outflow moves out of WY/CO and interacts with stronger
instability over the Dakotas overnight. Given the lack of low-level
jet support and uncertainty, will maintain 5% probabilities.
...Four Corners Region...
Daytime heating combined with a midlevel moist plume and cooling
aloft should yield scattered afternoon development over far eastern
AZ and UT into western CO and NM. Instability will not be
particularly strong, but likely sufficient for a few damaging gusts
or marginal hail as the most prevalent storm mode is expected to be
cellular with favorably long hodographs/veering with height. Some of
this activity may persist well into the evening over NM.
..Jewell/Squitieri.. 09/12/2025
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