Mesoscale Discussion 1278

Issued

Jul 13, 2021, 10:30 PM MDT (04:30 UTC)

Expired

Jul 14, 2021, 12:00 AM MDT

In force

90 min

Issued by

the Storm Prediction Center

Concerning

Severe thunderstorm watch 376

Counties Banner County, NE, Box Butte County, NE, Cheyenne County, NE, Dawes County, NE, Garden County, NE, Grant County, NE, Morrill County, NE, Scotts Bluff County, NE, Sheridan County, NE, Sioux County, NE, Bennett County, SD, Custer County, SD, Fall River County, SD, Jackson County, SD, Lawrence County, SD, Meade County, SD, Oglala Lakota County, SD, Pennington County, SD, Goshen County, WY

The Rapid City radar (KUDX), 105 km from the middle of the area, began a volume at 04:32 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

642 
ACUS11 KWNS 140430
SWOMCD
SPC MCD 140430 
NEZ000-SDZ000-WYZ000-140600-

Mesoscale Discussion 1278
NWS Storm Prediction Center Norman OK
1130 PM CDT Tue Jul 13 2021

Areas affected...Far easter WY...Southwest SD...Western NE Panhandle

Concerning...Severe Thunderstorm Watch 376...

Valid 140430Z - 140600Z

The severe weather threat for Severe Thunderstorm Watch 376
continues.

SUMMARY...Strong to severe gusts are possible across far southeast
WY, southwest SD, and the western NE Panhandle for the next hour or
so. Isolated hail could also occur. The need for a downstream watch
is uncertain, but trends are being monitored.

DISCUSSION...Two distinct thunderstorms clusters continue to evolve
eastward/southeastward into southwest SD and the western NE
Panhandle. Northernmost cluster moving into southwest SD has
recently shown some new updrafts on its southwestern flank over
Weston County WY as well as a modest increase in the overall forward
progression of the cluster. Storm motion of the cluster also appears
to have taken a more southerly component. These trends will likely
continue given the more buoyant air mass in place south of the
evolving line. Strong to severe gusts have been measured within this
line and the expectation is for the damaging wind threat to persist
as it move southward/southeastward.

Southernmost cluster has recently shown a marked increase in updraft
strength, particularly across its central and southern region (over
Sioux and Scotts Bluff Counties in NE and Goshen County in WY). This
is likely a result of increasing buoyancy with southeastward extent.
Forward speed within the line has not noticeably increased yet.
However, given the noted updraft strengthening, an increase in
forward progression is likely. Low-level stability may temper the
wind gusts realized at the surface, but some strong to severe gusts
are still possible.

Given the nocturnal stabilization, the need for a downstream watch
is currently uncertain. However, convective trends will be monitored
closely for signs that coverage of severe gusts will be high enough
to merit watch issuance.

..Mosier.. 07/14/2021

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

ATTN...WFO...LBF...UNR...CYS...

LAT...LON   44050436 44650351 44630196 43840154 41780146 41160286
            41410460 44050436

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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.