Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1252 AM CDT Mon Jul 21 2025
Valid 211200Z - 221200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF CENTRAL
AND EASTERN MONTANA...
...SUMMARY...
Severe thunderstorms capable of producing severe wind gusts, large
hail, and perhaps a tornado or two are expected across parts of the
northern Great Plains. Additional isolated strong to severe storms
are possible in the central Plains.
...Synopsis...
Modest amplification of an upper-level ridge is expected across the
Plains into the Upper Midwest today. In the Northwest, the
upper-level trough will take on a more neutral tilt before
progressing eastward by Tuesday morning. At the surface, modest lee
troughing will be in place within the northern/central High Plains
regions. An outflow boundary is likely to be situated somewhere in
the North Dakota/South Dakota border vicinity. Farther east into
Minnesota, a warm front like feature will arc southeastward into the
lower Ohio Valley. Strong to extreme buoyancy is forecast to develop
within parts of the northern/central Plains.
...Montana into western North Dakota...
The highest confidence in the development of severe storms is within
the terrain of central Montana. Additional storms may develop in the
vicinity of the Big Horns and move into southeast Montana. Mid-level
heights will be rising through the morning/afternoon so initiation
could be somewhat delayed. Subtle mid-level height falls will occur
during the evening, however. With a belt of strong mid-level winds
across the region, initial storms should be supercellular. Large
hail and severe wind gusts will be the initial hazards. With storms
developing in somewhat drier air, it is possible they will be
outflow dominant and not maintain their cellular mode as they move
northeast into greater moisture. The environment will be
conditionally favorable for 2+ inch hail, but the spatial extent of
this threat is not certain. Severe wind gusts will likely become
more common later in the evening as activity grows upscale.
...Dakotas into Minnesota/Mid-Missouri Valley...
Two clusters of convection are ongoing in the Dakotas. Based on
current surface observations, this activity is expected to generally
move eastward along the North Dakota/South Dakota border. What
occurs with the outflow from this activity into this afternoon will
play a role in the severe potential within parts of the Dakotas.
Strong to extreme buoyancy will be present south of the outflow.
Forcing for ascent will be weak. Storm development will depend on
the timing of the early morning convection and subsequent
heating/mesoscale lift during the afternoon. A weak surface low in
western South Dakota may lead to some locally enhanced convergence
along the outflow and trigger storms. This scenario is also not
certain.
Effective shear of 40-45 kts and MLCAPE likely above 4000 J/kg will
support intense, organized storms. Initial storms would be capable
large hail, severe winds, and perhaps a tornado or two. Storms that
do develop would eventually grow upscale and potentially produce a
swatch of severe winds. Model guidance varies on the timing/location
of this activity. There is some potential for a cluster/MCS to
propagate along the warm front feature into central Minnesota. Other
solutions show the MCS moving into the greater buoyancy toward the
Mid-Missouri Valley. Given some capping can be expected, storms may
not develop at all. The marginal risk has been expanded to account
for these possibilities, but confidence remains too low for a
categorical upgrade at this time.
...Central High Plains...
Strong heating near the surface trough should promote isolated to
widely scattered storms from the Palmer Divide into the Nebraska
Panhandle. Effective shear of 25-30 kts (generally weaker with
southern extent) will allow for marginally organized storms. Severe
wind gusts are the main concern as storms develop in the drier air.
Some potential for large hail may also exist if storms can persist
into greater moisture to the east.
..Wendt/Dean.. 07/21/2025
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