Severe Thunderstorm Warning 129, NWS Cheyenne, WY

Area Forecast Discussion
National Weather Service Cheyenne WY
214 PM MDT Mon Jun 22 2026

.KEY MESSAGES...

- Scattered strong to severe afternoon and evening thunderstorms
  are expected today, mainly east of I-25. While all severe
  hazards are possible today, large hail is the primary concern.

- Widely scattered strong to severe thunderstorms are possible
  again on Tuesday, mainly south of the North Platte River.

- Thunderstorm chances continue on Wednesday and Thursday with
  greater coverage storms increasing the potential for localized
  flooding concerns, particularly over recent burn scars.

- Warming temperatures, falling humidity, and increasing winds
  will increase fire weather concerns this weekend.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 215 PM MDT Mon Jun 22 2026

Another round of active weather is anticipated today across the
area. The morning deck of low clouds burned off quite quickly this
morning. We still have a little bit of MLCIN remaining in the
central and norther Nebraska panhandle, but this continues to
weaken. Otherwise, a fairly potent convective environment is present
across the area early this afternoon. A sharp dryline is locked up
against the Laramie Range as a surface high with plentiful moisture
flux from the southeast remains in place to the east. An upper level
low well to our north is carrying a modest upper level jet streak
with it which is supporting strong deep layer shear over the area.
Effective bulk shear is around 40 to 50 knots at this time, and is
progged to increase gradually through the evening, locally exceeding
60 knots later. Ample instability is also present, with MLCAPE 1000
to 1500 J/kg already, and expected to increase closer to 2000 J/kg
later this afternoon. This sets the stage for scattered strong to
severe thunderstorms today. Coverage will not be all that high
today, but there is potential for several discrete supercells. The
primary concern is large to very large hail, but these types of
storms are capable of producing all severe weather hazards,
including a few tornadoes, strong winds, and localized flash
flooding. The tornado risk will increase later in the afternoon into
the early evening as a surge of the low-level jet enhances the low-
level wind shear, but confidence is lower in the tornado threat. A
Severe Thunderstorm Watch is in effect until 8PM today, but portions
of the area may see a strong storm lingering for another hour
or two after that. While the watch includes the I-25 counties,
the primary concern is east of the I-25 corridor. We will also
need to watch for a storm passing directly over the South Fork
fire burn area, as today's storms will produce locally heavy
rainfall, and thus a limited flash flood concern over the fresh
burn scar.

Overnight tonight, the shortwave trough passing to our north will
continue to produce overrunning ascent as a surface cool front tries
to push southward. Elevated instability will continue through the
night as well. Hi-res models are in good agreement showing fairly
widespread activity across south Dakota, but parameters are
generally not too different for our area. While hi-res models don't
show much here, the forcing and parameters are enough to keep 20 to
40% PoPs running through the night along and north of the North
Platte River valley. The overnight moisture return will have the
potential to produce patchy morning fog and low clouds once again to
begin Tuesday. Expect to start off the day with breezy north to
northeast winds as well.

Tuesday will have a somewhat different setup across the area in the
wake of tonight's cool front. Decent upslope flow will keep cooler
and moist conditions in place over much of the High Plains. Expect a
strong cap to develop over much of the area. South of the North
Platte River valley, the cap will be a bit weaker, and thus more
likely to erode later in the day. As a result, the primary area of
concern is in southeast Wyoming along the I-80 corridor (plus Platte
County). This could extend into Goshen and the southern panhandle,
but confidence is lower there. As today, the primary concern will be
large hail once again.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 215 PM MDT Mon Jun 22 2026

Wednesday...West northwest flow aloft continues, while a shortwave
trough aloft moves over eastern Wyoming near peak heating. A decent
low level convergence boundary will stretch across southeast Wyoming
in the afternoon, with an 850 and 700 mb theta-e ridge axis
extending from Casper to Cheyenne. Expecting scattered afternoon and
evening thunderstorms to initiate in the convergence boundary, and
with CAPE of 1000 to 2000 J/kg and bulk shear values near 45 knots,
we should see isolated to scattered strong to severe thunderstorms
develop from afternoon through early evening, and concur with the
Storm Prediction Center outlook of marginal to slight risk over our
eastern half of counties.

Thursday...Westerly flow aloft continues, and with surface low
pressure developing over south central Wyoming producing a
convergence axis from Douglas to Laramie, and plenty of low and mid
level moisture, and 850/700 mb theta-e ridge axis from Casper to
Cheyenne, along with CAPE of 1000 to 1800 J/kg and bulk shear near
50 knots, we anticipate some storms to become severe, with large
hail and damaging winds as the primary threats east of I-25, with
some locally heavy rainers due to flow aloft.

Friday...Low amplitude ridging develops over our forecast area, with
some drier air noted advecting in. However, still expect isolated to
widely scattered afternoon and evening thunderstorms to form along a
low level convergence axis along the I-25 corridor. A few strong and
possibly severe storms may occur.

Saturday...The flow aloft turns southwest and increases in speed,
with considerably drier air moving across our counties, producing a
dry day with a warming trend as 700 mb temperatures spike near 19
Celsius.

Sunday and Monday...A broad trough aloft develops across the
northern and central Rockies, with dry southwest flow aloft, leading
to only isolated to widely scattered thunderstorms in the afternoons
and evening. Slightly cooler compared to Saturday in the wake of a
cold frontal passage.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1107 AM MDT Mon Jun 22 2026

A weather disturbance aloft will move over western Nebraska late this
afternoon and will combine with adequate low and mid level moisture
to produce isolated to scattered afternoon and evening thunderstorms
today across far southeast Wyoming and the Nebraska Panhandle.

Widespread low clouds and fog will occur after midnight tonight along and
east of I-25 including TAF sites at Cheyenne and the Nebraska Panhandle.
MVFR ceilings will continue much of Tuesday morning for TAF sites east
of I-25.

Wyoming TAFS...High confidence in VFR at Laramie and Rawlins, with
sufficient surface gradients to produce wind gusts to 30 knots until 01Z.

For Cheyenne, high confidence in VFR through 08Z, with IFR in low clouds
and fog thereafter and ceilings rising to MVFR after mid morning Tuesday.
Sufficient surface gradients to produce wind gusts to 26 knots until 01Z.

Nebraska TAFS...High confidence in VFR continuing until around 08Z, with
isolated to scattered thunderstorms at each site from 20Z to 02Z,
producing a few wind gusts in excess of 45 knots and visibilities under
three miles at times. High confidence in widespread IFR developing
after 08Z, due to ceiling and visibility restrictions. Visibilities will
improve above six miles after 15Z Tuesday, with ceilings improving to
MVFR.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.

&&

SHORT TERM...MN
LONG TERM...RUBIN
AVIATION...RUBIN

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