ACUS11 KWNS 080428
SWOMCD
SPC MCD 080428
IAZ000-SDZ000-NEZ000-080630-

Mesoscale Discussion 2269
NWS Storm Prediction Center Norman OK
1128 PM CDT Mon Sep 07 2026

Areas affected...parts of southeastern South Dakota...northeastern
Nebraska and adjacent portions of the middle Missouri Valley

Concerning...Severe Thunderstorm Watch 664...

Valid 080428Z - 080630Z

The severe weather threat for Severe Thunderstorm Watch 664
continues.

SUMMARY...Localized strong wind gusts remain possible in lingering
thunderstorm development, but the risk for severe weather, in
general, appears to be waning. A new severe weather watch is not
anticipated, but trends will continue to be monitored.

DISCUSSION...Warm advection along a convective outflow reinforced, quasi-stationary low-level baroclinic zone, aided by a 40-45+ kt
southerly 850 mb jet, has been providing support for a persistent
band of convection. This has been focused southeast of Chamberlain
through the Yankton vicinity, with perhaps some northward/eastward
drift to the north of the Missouri River the past hour or two.

Forecast soundings near this activity indicate the lingering
presence of some combination of remnant elevated mixed-layer air and
subsidence induced warming/drying in the the 850-700 mb layer.
Entrainment of this air, and subsequent evaporative cooling and
downward mixing of momentum, may have provided support for an
eastward surging segment/small evolving cluster overspreading the
Yankton vicinity. However, lapse rates near and just above the
surface appear to have become stable enough to limit much more than
rather localized strong surface gust potential. And this potential
seems likely to wane further with continuing convective development
into the 06-07Z time frame.

..Kerr.. 09/08/2026

...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fjg!8WPU86JtbxJNrts7aMo7sfIlcceZObw-YZnl0HLIVX3fVwRPmuoHVxo-FTsSsbzvlXEKD1yCR0WvC4cborsZKwjWAEs$ for graphic product...

ATTN...WFO...FSD...OAX...LBF...

LAT...LON 43359871 43459690 43209637 42739653 42659729 42859897
43359871

MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN


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