ACUS01 KWNS 111206
SWODY1
SPC AC 111205

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0705 AM CDT Thu Sep 11 2025

Valid 111300Z - 121200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM EASTERN
MONTANA INTO WESTERN NORTH DAKOTA...

...SUMMARY...
Scattered severe thunderstorms are possible over eastern Montana
into western North Dakota late this afternoon through the evening.
The primary hazards are severe gusts and large hail.

...Synopsis...
Water-vapor imagery shows a large cyclone over the West with a
downstream ridge over the Great Plains, and a trough centered over
the Lower Great Lakes.  Southwesterly mid to high-level flow extends
from the base of the larger-scale western U.S. trough northeastward
through the Great Basin and into the northern Great Plains.  A
mid-level disturbance implied in morning water-vapor imagery over
western WY, is forecast to move northeast into eastern MT/western ND
towards this evening.

In the low levels, a plume of seasonably rich moisture will protrude
northward from the central Plains into the Dakotas and eastern MT.
A lee trough will extend southward from a surface low over the
northern High Plains.

...Rockies into the northern Plains...
An ongoing cluster of weak thunderstorms associated with warm-air
advection near the ND/Manitoba border will continue to move
east-northeastward into southern Canada ahead of a pair of MCVs over
western ND/eastern MT.  Diurnal heating over the higher terrain from
near the Four Corners northward into southern MT will favor
scattered thunderstorms developing during the midday into the early
afternoon.  Storm coverage will probably increase further over the
central Rockies during the afternoon, with the stronger storms
capable of an isolated hail/wind threat.  As the airmass
destabilizes over the plains, particularly across eastern MT within
the moist plume primarily north of the surface low, isolated to
scattered storms are forecast by mid to late afternoon.  This
initial activity will probably develop near the MT/WY border with
upscale growth into a cluster possible during the evening.
Deep-layer shear supporting organized storm modes coupled with steep
lapse rates, will combine to aid in several stronger storms capable
of a hail/wind threat.  The wind threat will probably continue into
ND during the evening within the terminus region of a 35-40 kt
southerly LLJ.  A gradual transition to increasingly elevated
convection is expected late as convective inhibition increases and
the overall severe risk lessens.

..Smith/Broyles.. 09/11/2025

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