Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1255 AM CDT Thu Sep 11 2025
Valid 111200Z - 121200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM EASTERN
MONTANA INTO WESTERN NORTH DAKOTA...
...SUMMARY...
A corridor of strong to severe thunderstorms with hail and damaging
gusts are expected from eastern Montana into western North Dakota,
while isolated/localized wind or marginal hail will be possible
across a large portion of the Rockies.
...Synopsis...
A large, positive-tilt upper trough will remain nearly stationary
across the western CONUS, with axis extending from western NV into
southern MB/SK. East of this trough, a broad fetch of 30-40 kt 500
mb southwesterlies will affect much of the Rockies and disturbances
rounding the upper ridge into the northern Plains.
At the surface, high pressure will maintain stable conditions over
much of the East, where a elongated/weak upper trough will exist.
Southerly surface winds will maintain a low-level moist plume across
the MO Valley with 60s F dewpoints, with 50s F into much of eastern
MT where surface winds will back to southeasterly.
The combination of daytime heating and substantial southwest flow
aloft across a large part of the Rockies, along with at least
marginal instability over a wide area suggest sporadic strong to
severe storms will be possible during the afternoon and evening.
...Rockies into the northern Plains...
Lapse rates will steepen over the area as heating commences, and
with the 500 mb -10 C isotherm extending from SD to southern UT. By
virtue of an uncapped air mass, sporadic afternoon storms are likely
over the higher terrain over northwest NM, CO, and over much of ID
into MT, while warm and drier air will generally be found from UT
into parts of central WY. However, even in the drier areas, a few
storms are likely as weak levels of instability develop.
Conditionally, the entire region will have deep-layer shear at or
above 35-40 kt, which will favor cellular storm mode. Small hail
appears most likely over much of the Intermountain West, with
locally strong gusts as well.
A potentially greater severe threat will extend from eastern MT and
WY into the western Dakotas, where moisture and instability will be
greater. A surface low is expected over southeast MT/northwest SD,
with backed/moist winds wrapping west. Forecast soundings in this
area depict robust CAPE profiles and hodographs favoring cells
producing hail, or perhaps bowing structures with both wind and hail
risk. Storms may form over south-central MT/northern WY after 21Z,
moving into the western Dakotas during the evening.
..Jewell/Wendt.. 09/11/2025
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