Mesoscale Discussion 891

Issued

Jun 8, 2021, 6:37 PM MDT (00:37 UTC)

Expired

Jun 8, 2021, 8:00 PM MDT

In force

83 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

40%

Counties Butte County, SD, Custer County, SD, Fall River County, SD, Lawrence County, SD, Meade County, SD, Pennington County, SD, Crook County, WY, Niobrara County, WY, Platte County, WY, Weston County, WY

The Rapid City radar (KUDX), 88 km from the middle of the area, began a volume at 00:37 UTC, the scan nearest the moment this went out.

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• Severe Thunderstorm Watch 249Jun 8, 7:00 PM MDT

225 
ACUS11 KWNS 090038
SWOMCD
SPC MCD 090037 
SDZ000-NEZ000-MTZ000-WYZ000-090200-

Mesoscale Discussion 0891
NWS Storm Prediction Center Norman OK
0737 PM CDT Tue Jun 08 2021

Areas affected...Eastern Wyoming western South Dakota and the
western Nebraska Panhandle.

Concerning...Severe potential...Watch possible 

Valid 090037Z - 090200Z

Probability of Watch Issuance...40 percent

SUMMARY...New storm development across eastern Wyoming may pose a
risk for severe winds later this evening across South Dakota and
western Nebraska. Considerable uncertainty on storm severity remains
given southward surging outflow and the high-based nature of storms.
A weather watch may be needed.

DISCUSSION...Evening water vapor imagery showed a compact shortwave
trough ejecting across the central Rockies and far western High
Plains. Ascent and stronger flow aloft from this trough has begun to
overspread the western edges of the warm and unstable airmass across
eastern Wyoming. Recent RADAR and satellite trends have shown an
increase in convective coverage/strength in the last 30 min.
Plentiful buoyancy (2000-3000 J/kg of MLCAPE) from SPC mesoanalysis
will support robust updrafts as high-based storms across eastern
Wyoming continue to develop eastward into deeper moisture this
evening. Given the deep and well-mixed PBL, damaging wind gusts
appear to be the primary threat. Large hail, while initially
limited, may become a greater threat later this evening as storms
encounter greater buoyancy farther east. However, weak vertical
shear( 20-30 kts) and a tendency to grow upscale may limit the
potential for larger hail.

To the north and east, a cluster of storms ongoing across
southwestern North Dakota may also interfere with developing
convection in the next couple of hours. Southwestward surging
outflow will tend to undercut storms as they move eastward casting
doubt on how widespread of a severe threat may develop. Regardless,
with large buoyancy and the potential for strong downdrafts, some
severe risk will likely develop this evening. A watch may be needed
should intensification trends continue.

..Lyons/Thompson.. 06/09/2021

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

ATTN...WFO...UNR...CYS...BYZ...

LAT...LON   41990471 42190525 43260516 44370528 45440411 45570305
            45390245 45090173 43820177 43170286 42740330 42400386
            41990471

Mesoscale Discussions in South Dakota, 2021Mesoscale Discussions in Wyoming, 2021Every mesoscale discussion in 2021

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.