Mesoscale Discussion 1583

Issued

Aug 23, 2021, 7:38 PM CDT (00:38 UTC)

Expired

Aug 23, 2021, 9:45 PM CDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe thunderstorm watch 458

The Aberdeen radar (KABR), 141 km from the middle of the area, began a volume at 00:39 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

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• Severe Thunderstorm Watch 459Aug 23, 10:10 PM CDT

462 
ACUS11 KWNS 240038
SWOMCD
SPC MCD 240038 
SDZ000-NDZ000-240245-

Mesoscale Discussion 1583
NWS Storm Prediction Center Norman OK
0738 PM CDT Mon Aug 23 2021

Areas affected...Central South Dakota and southern North Dakota

Concerning...Severe Thunderstorm Watch 458...

Valid 240038Z - 240245Z

The severe weather threat for Severe Thunderstorm Watch 458
continues.

SUMMARY...The severe thunderstorm threat continues across WW 458 in
south-central South Dakota. A favorable environment for isolated
strong to severe storms is developing across northern South Dakota
and southern North Dakota. Trends are being monitored across this
region.

DISCUSSION...Latest radar trends from South Dakota show a few
isolated cells ongoing within and on the periphery of WW 458. These
storms have exhibited periods of supercellular characteristics with
strong hail signatures (via MRSM MESH and vertically integrated ice
estimates), though thunderstorm coverage has been limited with some
weakening trends noted in the last half hour. This may be the result
of somewhat weak forcing for ascent coupled with the onset of
diurnal cooling. However, water vapor imagery suggests that stronger
lift associated with an upper-level impulse remains upstream across
CO/WY. Modest, but persistent, surface pressure falls over the High
Plains over the past 2 hours support this idea and hint that more
favorable broad-scale lift may overspread the region in the coming
hours. Recent HRRR guidance loosely captures this scenario, which is
supported by the aforementioned observed trends and points towards a
continuation of the severe threat at least through the evening
hours. 

Further north, gradual destabilization is noted as MUCAPE values
increase to above 1000 J/kg along the ND/SD border due to low to
mid-level moisture transport to the north/northwest. Weak convection
moving out of northwest SD into this environment may undergo
intensification given the favorable instability, strong deep layer
shear (nearly 50 knots effective bulk shear sampled by the 00z BIS
and ABR soundings), and increasing lift through the evening (via
isentropic ascent in the 850-700 mb layer). While confidence in
storm coverage is somewhat uncertain, convective trends in this area
will be monitored.

..Moore.. 08/24/2021

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

ATTN...WFO...FSD...ABR...BIS...UNR...

LAT...LON   43300088 44070163 45490208 46320209 46630142 46710027
            46499941 45879860 45119809 44239802 43649806 43339853
            43029953 43300088

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The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.