South Dakota Mesoscale Discussion

Areas affected…portions of North Dakota and South Dakota

Concerning…Severe potential…Watch likely

Valid 251950Z – 252145Z

Probability of Watch Issuance…80 percent

SUMMARY…Observational trends and model guidance suggest that a
Severe Thunderstorm Watch will be needed by around 21Z or so.

DISCUSSION…Latest objective analyses and satellite imagery
suggests a destabilizing atmosphere especially across western
portions of the discussion area, with insolation now yielding
towering cumulus near/east of ISN through west of BIS. Warming
surface temperatures (into the 80s F) was contributing to MUCAPE
values around 2000-3000 J/kg amidst steep (7-8C/km) mid-level lapse
rates and modest (30-40 kt) deep shear. Meanwhile, a weak mid-level
shortwave trough over eastern Montana was approaching the region
from the west, which should provide additional ascent/cooling aloft
and further aid in convective initiation. The region also resides
beneath the exit region of a gradually strengthening mid-level jet
that should impinge on the region through tonight.

Latest thinking is that storms will continue to increase in coverage
and intensity over the course of the afternoon and will likely grow
upscale into a mix of cells and clusters as cold pools mature amidst
modest low-level shear. Severe hail and damaging wind gusts will be
the most probable threats with this activity. The threat will be
widespread enough to necessitate a WW issuance, and this will be
coordinated with affected WFOs during the 20-21Z window.

..Cook/Thompson.. 08/25/2019

…Please see for graphic product…


LAT…LON 48930223 49150150 49080000 48469939 46859919 44819915
43639967 43260028 43250116 43330191 43710260 44790309
45810302 47560273 48930223

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