ACUS11 KWNS 230444
SWOMCD
SPC MCD 230444=20
NEZ000-SDZ000-WYZ000-230645-

Mesoscale Discussion 1266
NWS Storm Prediction Center Norman OK
1144 PM CDT Mon Jun 22 2026

Areas affected...eastern Wyoming...southwest South Dakota...and
northwest into north-central Nebraska

Concerning...Severe potential...Watch unlikely=20

Valid 230444Z - 230645Z

Probability of Watch Issuance...20 percent

SUMMARY...Thunderstorms will continue this evening across eastern
Wyoming, southwest South Dakota, and northwest into north-central
Nebraska. Isolated large hail will be possible in the short term,
with an increasing wind threat perhaps evolving overnight. A watch
is not likely in the short-term, but the region will be monitored
for a watch overnight.

DISCUSSION...Thunderstorms are developing or re-intensifying this
evening across the highlighted area. A report of 1.5" hail was
received around 10 PM MDT this evening across Oglala, South Dakota.
Examination of model soundings indicates a largely uncapped
atmosphere across the area. Evaluation of objective analyses
suggests broad warm-air advection centered on the 700-millibar layer
is likely contributing to the broad, large-scale ascent across the
area.

MUCAPE values have waned from earlier this evening, with current
values locally around 1000-1500 J/kg and most areas having less. Effective-layer shear remains greater than 50 knots across much of
the area, largely owing to the southeasterly low-level flow and the
broad westerly mid-level flow.=20

These thunderstorms should continue to percolate this evening into
the morning hours as they generally move east-southeast. Mid-level
lapse rates have weakened a bit from earlier today, with only around
7 C/km estimated from model soundings from the RAP analyses. This
would indicate a more limited potential for large hail, however,
very long, straight hodogaphs will support supercellular storm modes
with dynamic pressure perturbations within the mesocyclone
augmenting ascent and supporting a continued threat for hail.=20

Latest high-resolution guidance suggests that these thunderstorms
will grow upscale later this evening, organizing into one or more
mesoscale convective systems. As this occurs, an increase in
damaging wind potential may increase, as DCAPE values are on the
order of 500-1000 J/kg.=20

The need for a watch should remain rather limited in the near term
given the small spatial/temporal scales of any large hail threat.
The need for a watch later tonight remains less certain owing to
differences in the guidance regarding any upscale evolution into an
MCS. The area will continue to be monitored.

..Marsh/Smith.. 06/23/2026

...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!_6wfM7GEUuWZj5pa7npxYHFgBekBUQ-1-BsOotE_1uTHZcY-95oUdWldSO7kb3_eiqL9Mz53H= mI1Q5-rTPmOju3ehw4$ for graphic product...

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

LAT...LON 43260036 42740006 42159994 41700036 41520148 41790241
42010295 42660464 43400569 44050625 44590595 44820507
44560381 44070244 43680135 43260036=20

MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN


=3D =3D =3D
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