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Mesoscale Discussion 1358
NWS Storm Prediction Center Norman OK
0229 PM CDT Mon Jul 04 2022

Areas affected...Parts of southwestern through central Montana

Concerning...Severe potential...Watch possible 

Valid 041929Z - 042230Z

Probability of Watch Issuance...60 percent

SUMMARY...A corridor of intensifying organized thunderstorm
development, including sustained supercells, may evolve south of
Helena into the Lewistown vicinity through 4-6 PM MDT.  Trends are
being monitored, and it is possible that a severe weather watch may
eventually be needed.

DISCUSSION...Downstream of a mid-level low and associated troughing
slowly progressing inland of the Pacific Northwest coast,
large-scale ascent coupled with weak to modest boundary-layer
destabilization likely will contribute to increasing scattered
thunderstorm development across the mountains of western through
south central Montana during the next few hours.

Models indicate a corridor of strengthening lower/mid tropospheric
frontogenetic forcing and warm advection south of Helena toward the
Lewistown vicinity through 22-00Z.  This may provide the focus for
the more sustained and vigorous thunderstorm  activity, coincident
with the strongest deep-layer mean shear (40-50 kt) and ambient
west-southwesterly mean flow (around 30 kt).  With another several
hours of daytime heating, mixed-layer CAPE may increase in excess of
1000 J/kg, gradually contributing to an environment increasingly
conducive to evolution of isolated supercells with the potential to
produce severe hail and locally strong surface gusts.

..Kerr/Grams.. 07/04/2022

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...BYZ...TFX...MSO...

LAT...LON   47101113 47240924 46350951 45731184 46331279 47101113