Mesoscale Discussion 0979
NWS Storm Prediction Center Norman OK
0232 PM CDT Thu Jun 04 2026
Areas affected...portions the southeastern Montana into the Black
Hills
Concerning...Severe potential...Severe Thunderstorm Watch likely
Valid 041932Z - 042100Z
Probability of Watch Issuance...80 percent
SUMMARY...Scattered strong to severe thunderstorms will develop
eastward through the afternoon, with large to very large hail and
strong/severe wind gusts the main hazards. A Severe Thunderstorm
Watch will likely be needed for a portion of the discussion area.
DISCUSSION...Moist, southeasterly flow north of a quasi-stationary
surface boundary and continued surface heating are contributing to
steepening low-level lapse rates and eroding MLCIN across portions
of the northern High Plains as of early this afternoon. Coupled with
increasing ascent ahead of an approaching mid-level shortwave
trough, this is promoting gradual thunderstorm development across
southeastern Montana and northeastern Wyoming, with deepening
cumulus also noted along portions of the Black Hills. As this
activity evolves eastward through the afternoon, two different
regimes of severe potential appear likely.
In the Black Hills vicinity, western/central South Dakota, and
northwestern Nebraska along and north of the surface boundary,
modestly strong westerly flow aloft (35-40 kts sampled at 4-5 km AGL
by the BLX/RIW VAD profiles) and effective shear of 35-45 kts are
likely to overlap greater low-level moisture and moderate buoyancy
(MLCAPE around 1000-2000 J/kg), with occasional supercells possible.
Coupled with steep mid-level lapse rates (700-500 mb lapse rate of
8.7 C/km sampled by the 18z UNR observed sounding) and elongated
hodographs, this should support large to very large hail as the
primary threat. Meanwhile, latest guidance and objective analysis
depicts marginally weaker effective shear (around 25-35 kts) and
steeper low-level lapse rates farther to the north across portions
of eastern Montana into southwestern South Dakota. This would favor
upscale growth along developing cold pools, with a more
multicellular storm mode and greater risk for strong to severe wind
gusts.
Trends will continue to be monitored, and watch issuance will likely
be needed for a portion of the discussion area to cover these
threats.
..Chalmers/Mosier.. 06/04/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...BIS...LBF...UNR...CYS...BYZ...GGW...
LAT...LON 44050566 44700590 45420596 46080589 46630550 46990469
47200376 47120307 46960267 46600228 46110206 44910200
43990199 43250200 42870201 42590212 42320225 42180243
42150271 42170310 42220361 42500419 43150505 44050566
MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN
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