SPC MD 1257
MD 1257 CONCERNING SEVERE THUNDERSTORM WATCH 376... FOR EASTERN WYOMING AND ADJACENT PORTIONS OF NEBRASKA...SOUTH DAKOTA AND FAR SOUTHEAST MONTANA

Mesoscale Discussion 1257
NWS Storm Prediction Center Norman OK
0310 PM CDT Mon Jun 22 2026

Areas affected...Eastern Wyoming and adjacent portions of
Nebraska...South Dakota and far southeast Montana

Concerning...Severe Thunderstorm Watch 376...

Valid 222010Z - 222215Z

The severe weather threat for Severe Thunderstorm Watch 376
continues.

SUMMARY...The threat for large hail is slowly increasing across
eastern Wyoming and far western Nebraska. This threat will gradually
spread east/southeast over the next few hours.

DISCUSSION...Latest GOES IR and MRMS data shows steady
intensification of a trio of supercells near the Sheridan, WY area
along with more isolated cells near Douglas, WY and near Kimball,
NE. Across north/northeast WY, low-level moisture is more limited,
but increasing ascent associated with the left-exit region of the
300 mb jet aloft continues to overspread the region, aiding in
mid-level cooling and compensating for the otherwise modest
moisture. This ascent will continue to promote storm intensification
through early evening as cells spread east/southeast. Recent
forecast guidance and SARS estimate hail sizes hint that hail sizes
will most likely reach into the 1-2 inch range over the next couple
of hours. 

Further south, storms in east-central WY to far western NE continue
to propagate into a plume of richer low-level moisture (dewpoints in
the low to mid 50s) where a regional SBCAPE maximum is noted (near
2000 J/kg). Continued low-level moisture advection coupled with
increasing mid-level flow attendant to the upstream mid-level wave
should further augment the convective environment over the next few
hours. By the 22-00 UTC period, the highest SHIP values should
reside from eastern WY into western NE, suggesting that the greatest
potential for 2-3 inch hail may manifest across this region.

..Moore.. 06/22/2026

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

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

LAT...LON   41020409 41600441 42690516 43860632 44660688 44990684
            45300658 45400596 45320544 44630469 43310368 42520320
            41580272 41180270 41030280 40820328 40790367 40830389
            41020409 

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

Read more
https://www.spc.noaa.gov/products/md/md1257.html