Mesoscale Discussion 1650

Issued

Aug 30, 2021, 1:50 PM MDT (19:50 UTC)

Expired

Aug 30, 2021, 3:45 PM MDT

In force

115 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

40%

Counties Dawes County, NE, Sheridan 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

• Severe Thunderstorm Watch 477Aug 30, 3:05 PM MDT

362 
ACUS11 KWNS 301951
SWOMCD
SPC MCD 301950 
NEZ000-SDZ000-WYZ000-302145-

Mesoscale Discussion 1650
NWS Storm Prediction Center Norman OK
0250 PM CDT Mon Aug 30 2021

Areas affected...Southwestern South Dakota and portions of far
northern Nebraska and eastern Wyoming

Concerning...Severe potential...Watch possible 

Valid 301950Z - 302145Z

Probability of Watch Issuance...40 percent

SUMMARY...A few severe thunderstorms, including supercells, with the
potential for damaging winds and hail are possible this
afternoon/evening. A weather watch is being considered.

DISCUSSION...As of 1930 UTC, visible imagery showed deepening
updrafts across the Black Hills of far western South Dakota and
eastern Wyoming. Developing within a weakly forced upper air regime,
additional surface heating and weak upslope flow are expected to
support continued destabilization and subsequent thunderstorm
development this afternoon. 

The modified 18z UNR sounding shows an environment potentially
conducive to organized multicells and supercells, with 1700 J/kg of
MLCAPE and 31 kt effective shear. Although weak, inhibition of -40
to -50 J/kg remains across the region, with low-level cumulus still
absent across far southwestern South Dakota. However, this will
likely be overcome in the next couple of hours as convective
temperatures in the mid to upper 80s F are breached by strong
surface heating. Isolated thunderstorm development is possible by
late afternoon as the incipient updrafts move out of the Black Hills
and onto the surrounding High Plains. Favorable CAPE/shear profiles
and mid-level lapse rates in excess of 8 C/km will support the
potential for large hail and damaging wind gusts, especially with
any supercells. 

While the environment will remain potentially favorable for severe
weather, uncertainty remains on the exact spatial coverage of storms
within the weak forcing regime. Hi-res guidance suggests that at
least isolated storms will develop and track southeastward into
northwestern Nebraska this evening. Given the favorable CAPE/shear
overlap an isolated severe risk for wind and hail would be possible.
Convective trends are being monitored for a possible weather watch
despite the uncertainty on storm coverage.

..Lyons/Grams.. 08/30/2021

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

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

LAT...LON   44790333 44600236 44130157 43750127 43380097 43020090
            42770100 42420145 42280212 42270267 42590352 42980384
            43420411 44030425 44440421 44670399 44790333

Mesoscale Discussions in South Dakota, 2021Mesoscale Discussions in Nebraska, 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.