Severe Thunderstorm Warning 25, NWS Cheyenne, WY

Area Forecast Discussion
National Weather Service Cheyenne WY
332 PM MDT Sat May 30 2026

.KEY MESSAGES...

- An unsettled weather pattern will continue this weekend with
  daily chances for afternoon/evening showers and thunderstorms
  as a potent upper level disturbance moves northeast over the
  area.

- Strong to severe thunderstorms will develop this afternoon for
  areas east of the I-25 corridor. If severe thunderstorms
  develop all hazards are possible; large hail, damaging winds,
  and tornadoes are possible.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 215 PM MDT Sat May 30 2026

Primary forecast concern over the next 48 hours is the potential
for severe thunderstorms over far eastern Wyoming and western
Nebraska this afternoon through late this evening. Potent upper
level low clearly seen on IR and Visible Satellite over south
central Wyoming is forecast to become a negatively tilted open
wave trough over the next several hours. This trough axis will
accelerate northward over eastern Wyoming and western Nebraska
through early this evening. Current surface observations show
ample moisture east of a line from Lusk Pine Bluffs,
paralleling the Wyoming/Nebraska border. Activity has already
started to form across far east central Wyoming and the northern
Nebraska Panhandle where low clouds have dissipated earlier in
the day. Further south, expect another round of thunderstorms to
push across far southeast Wyoming and the southern Nebraska
panhandle, which are now starting to form south of the
Wyoming/Colorado border at this hour. This area will likely
become our primary focus as it moves northeast into this
evening. Upper level analysis shows strong upper level
diffluence increasing rapidly late this afternoon along and
east of I-25 as the base of the trough/vort max lifts northeast.
Expect multicells and isolated supercells initially, with
activity growing upscale once the vort max lifts north. Overall,
expect a large hail threat (1.00-2.00 inches) and maybe an
isolated tornado becoming a straight line wind threat through
the evening hours. Could see some gusts up to 75 MPH with the
strongest lines. A Severe Thunderstorm Watch has been issued
mainly for areas east of Interstate 25 until 900 PM late this
evening. Although cells will move north and northeast, expect
any lines of thunderstorms to propagate eastward into this
evening.

Further west, moisture is much more limited with dewpoints
already dropping into the 30s this afternoon. Still expect
isolated to widely scattered thunderstorms with a gusty wind
threat into this evening before the cooler air, associated with
the negatively tilted trough, moves east into central Wyoming.
Once the trough lifts northeast, westerly winds will increase
behind it with most models showing 700mb winds around 50 knots.
In-house wind guidance shows 55% to 65% probability of high
wind criteria for Arlington/Elk Mountain, with probabilities
between 30% to 45% for Bordeaux and the I-80 Summit/foothills.
With shallow convection over the Arlington area, and a
possibility for gusty winds, decided to upgrade the High Wind
Watch to a Warning and start it earlier (400 PM) in the day.

Thunderstorm activity should push east of our area by midnight,
with left over showers before sunrise Sunday. Can't rule out
some low clouds and patchy fog in areas that received heavy
rain, but westerly winds will quickly increase towards morning
limiting any fog threat. Other than High Wind concerns in and
near the wind prone areas and breezy conditions elsewhere, quiet
weather expected into Sunday with any thunderstorm activity
staying well to the north of I-80 towards Douglas and Lusk. Not
as cool with a slight warming trending...and high temperatures
in the upper 60s (west of I-25) to low/mid 80s for western
Nebraska.

For Monday, showers and thunderstorms should return to the high
plains as surface winds shift into the south and southeast.
Further west, another broad upper level trough will brush the
northern Great Basin region and move into Wyoming later in the
day. May see some strong to marginally severe thunderstorms with
0-6km shear around 35 knots and some low to midlevel
instability.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Issued at 231 PM MDT Fri May 29 2026

The long term will remain as unsettled as the short term with near
daily chances of precipitation through at least mid-week. With
the upper-level trough responsible for Saturday's storm expected
to eject northeastward out if the area Sunday, precipitation
chances on Sunday will be rather slim. Lingering showers could
be possible for the northern Wyoming and Nebraska zones of the
forecast area as the system ejects into the Dakotas, but even
these chances look rather slim.

Precipitation chances will increase for the start of the work week
as the upper-level trough/low begins to retrograde back towards the
northwest. The rough location of the low over the Montana/Canada
border, will allow the CWA to once again tap into moisture from the
Gulf. Moisture-rich mid-level southerly flow will usher in the
necessary humidity to fuel storm develop during the afternoon and
evening. Lift will come in the form of vorticity maxes streaming
through the area from the trough to the north, as well as another
trough the enters the picture during the middle of next week. At
this point, global models seem fairly consistent on showing daily
storm chances east of the Laramie Range Monday through Thursday. A
quick look at model soundings for areas east of the Laramie Range
show moderate amounts of CAPE each afternoon as well as decent shear
most days. As a result, severe weather cannot be ruled out each
afternoon.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1210 PM MDT Sat May 30 2026

Potent upper level low/trough will lift northeast across the area
today and tonight. Numerous showers and scattered thunderstorms will
develop across the mountains and move east into the high plains this
evening. Thunderstorms will likely become strong to severe for the
western Nebraska terminals and contain strong gusty winds, hail, and
brief very heavy rainfall.

HAZARDS/WEATHER TRENDS: VFR conditions should prevail at KRWL and
KLAR, although some periods of MVFR CIGS can't be ruled out tonight
with some rain shower activity. Further east, showers and
thunderstorms are expected to develop over the next few hours and
track northeast. There is a chance of IFR conditions with these
thunderstorms (15% to 25%), but impacts should be less than 2 hours.
Also, the terminals that see heavy rainfall amounts may see some fog
and/or low CIGS later this evening and into tonight. However
confidence is low (prob and coverage), so will keep out of the TAF
for now.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...

WY...High Wind Watch from 9 PM MDT this evening through Sunday
     afternoon for WYZ106-116-117.
     High Wind Warning until 9 AM MDT Sunday for WYZ110.

NE...None.

&&

SHORT TERM...TJT
LONG TERM...NB
AVIATION...TJT

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