Mesoscale Discussion 1419
NWS Storm Prediction Center Norman OK
0525 PM CDT Wed Aug 04 2021
Areas affected...Parts of northwestern into north central Montana
Concerning...Severe potential...Watch unlikely=20
Valid 042225Z - 050030Z
Probability of Watch Issuance...20 percent
SUMMARY...Strong thunderstorm development, including a few supercell structures, probably will continue near and north through east of
Cut Bank into 6-8 PM MDT time frame, posing a risk for severe hail
and locally strong surface gusts.
DISCUSSION...Vigorous thunderstorm development appears underway to
the northwest and north of Cut Bank. This is occurring within the
crest of large-scale mid-level ridging, where forcing for ascent,
associated with weak low-level upslope flow and an approaching
mid-level short wave trough migrating through the broader-scale
anticyclonic flow, may support the maintenance of convection into
the 00-02Z time frame.
A seasonably warm and deeply-mixed boundary layer (with 40+ F
surface temp/dew point spreads) across this region appears
characterized by modest CAPE on the order of 500-1000 J/kg.=20
However, within the cloud-bearing layer, mean flow may be in excess
of 30 kt, with unidirectional but strong westerly shear.
This environment may remain supportive of the formation of
additional splitting supercell structures with the potential to
produce severe hail and at least locally strong downbursts. It is
possible that consolidating surface cold pools could begin to
support some upscale convective growth, with a tendency to propagate south-southeastward accompanied by a bit more substantive risk for
strong surface gusts by early evening.
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