South Dakota Mesoscale Discussion

Areas affected…portions of extreme southeastern ND…extreme
northeastern SD…central/southern MN…western WI.

Concerning…Severe Thunderstorm Watch 632…

Valid 022325Z – 030100Z

The severe weather threat for Severe Thunderstorm Watch 632

SUMMARY…A severe bow echo and related complex of convection will
continue to translate southeastward across the remainder of watch
632 over the next 1-2 hours. The related severe-wind threat will
persist farther southeastward toward parts of western WI through the
evening, and another watch will be coordinated with affected local
NWS offices soon.

DISCUSSION…Surface mesoanalysis shows a warm front from
northwestern SD southeastward near a low over west-central SD, then
east-southeastward to eastward across the FSD area and extreme
northern IA. The warm front is forecast to move slowly northward
through the remainder of the evening. However, the air mass north
of the warm front only gradually stabilizes with northward extent at
the surface. That stable layer also is shallow, based on modified
model soundings and the ability of the complex to penetrate that
stable layer with multiple significant-severe gusts in Stutsman
County SD. Objective mesoanalysis data appear to be underdone with
MUCAPE north of the surface warm front, based on the behavior of the
convection so far.

The low levels above the shallow stable layer will become more
favorable as warm advection continues and perhaps strengthens
somewhat, with an intensifying preconvective LLJ in mass response to
the upshear shortwave trough aloft. Meanwhile, 45-60-kt
effective-shear vectors, aligned nearly parallel to the
theta-e/instability gradient, will support a continued southeastward
thrust of a cold pool that already is accompanied by a robust
thermal/isallobaric perturbation. Given these factors, another
severe thunderstorm watch will be required.

..Edwards.. 09/02/2019

…Please see for graphic product…


LAT…LON 46029867 46189773 46579691 47019667 47309666 47509679
46189235 45549116 44929129 44539198 44029320 44099439
44599564 45639766 45969838 46029867

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