ACUS11 KWNS 221730
SWOMCD
SPC MCD 221729=20
NEZ000-COZ000-SDZ000-WYZ000-MTZ000-221930-

Mesoscale Discussion 1254
NWS Storm Prediction Center Norman OK
1229 PM CDT Mon Jun 22 2026

Areas affected...Southeast Wyoming into adjacent portions of Nebraska...Colorado...South Dakota...and Montana

Concerning...Severe potential...Watch likely=20

Valid 221729Z - 221930Z

Probability of Watch Issuance...80 percent

SUMMARY...Thunderstorm development appears likely in the next couple
of hours across southeast Wyoming. Storms that develop will likely
mature into supercells posing a threat for very large hail; watch
issuance will likely be needed as convection begins to develop.

DISCUSSION...Latest GOES imagery shows a small zone of deepening
cumulus within a weak upslope flow regime along the eastern slopes
of the Laramie and Big Horn Mountains in Wyoming. Latest forecast
guidance suggests that lingering mixed-layer inhibition will be
largely eroded as temperatures warm into the mid to upper 70s. With
observed temperatures in the vicinity of the deepening cumulus
currently in the upper 60s and low 70s, it appears likely that
further growth will occur with increasing probability for convective
initiation over the next couple of hours - especially as broad-scale
ascent ahead of an upstream wave continues to overspread the region.


Regional VWPs are sampling 35-45 knot mid-level flow, which should
increase through late afternoon as the mid-level disturbance
continues to the southeast. This will yield elongated hodographs
with effective shear values on the order of 40-50 knots by late
afternoon, which will promote splitting supercells capable of
producing very large hail (possibly as high as 2.5 to 3 inches based
on sounding analogs). Large hail, as well as brief tornado,
potential appears highest across southeast WY into northeast
CO/western NE where richer low-level moisture will support higher
buoyancy and more intense updrafts and some effective SRH is noted
in latest RAP mesoanalyses. Trends are being monitored for the onset
of more substantial/widespread initiation, and watch issuance will
likely be needed once this becomes apparent.

..Moore/Hart.. 06/22/2026

...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!5lrSVYhrdQQO8m2eO9uevuENEGrvqKKT-p1_CcJ7nqCSYCVQG-LUNx5RgomQIoYLha2oC4TN0= rf1nDlF8R9yXakrhPQ$ for graphic product...

ATTN...WFO...UNR...BOU...CYS...BYZ...RIW...

LAT...LON 41040280 40490278 39840289 39590311 39480349 39450403
39500439 39730463 40170468 40510465 41030475 41240477
41800491 42580541 42900570 43580623 44400676 44930699
45230685 45270612 45120552 44710501 44140455 43370401
42610357 41460294 41040280=20

MOST PROBABLE PEAK TORNADO INTENSITY...85-110 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...2.00-3.50 IN


=3D =3D =3D
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