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Mesoscale Discussion 1399
NWS Storm Prediction Center Norman OK
0242 PM CDT Wed Jul 06 2022

Areas affected...southwestern through central Montana

Concerning...Severe potential...Watch likely 

Valid 061942Z - 062215Z

Probability of Watch Issuance...80 percent

SUMMARY...Isolated strong to severe thunderstorm development is
underway.  A more substantive increase in storms, including isolated
supercells, appears possible as early as 4-6 PM MDT, which may
require the issuance of a severe weather watch.

DISCUSSION...On the northwestern periphery of large-scale mid-level
ridging within the westerlies, a low amplitude short wave
perturbation is in the process of migrating north of the Great Basin
toward the northern Rockies.  Associated downstream forcing for
ascent is spreading across the mountains of western Montana, and may
be contributing to ongoing isolated thunderstorm initiation off the
higher terrain east-southeast of Great Falls and north of the
Yellowstone vicinity.  Otherwise, latest objective analysis suggests
that considerable inhibition remains for destabilizing mixed-layer
parcels.

During the next few hours, the inhibition will likely continue to
weaken in the presence of continued weak large-scale ascent and
further boundary-layer warming.  As this occurs, a corresponding
increase in thunderstorm development seems probable.  Beneath 30-40
kt southwesterly flow in the 500-300 mb layer, deep-layer shear is
sufficiently strong to support supercells, in the presence of
thermodynamic profiles characterized by steep mid-level lapse rates
and mixed-layer CAPE on the order of 1000-2000 J/kg.  This will be
acco*panied by the risk for large hail, locally strong surface gusts
and perhaps some potential for a tornado.

..Kerr/Grams.. 07/06/2022

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

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

LAT...LON   45701240 46191308 47511219 48211000 47160808 45390925
            45661079 45701240