Severe Thunderstorm Warning 154, NWS Cheyenne, WY

Area Forecast Discussion
National Weather Service Cheyenne WY
222 PM MDT Thu Jun 25 2026

.KEY MESSAGES...

- A Marginal Risk for strong to severe thunderstorms expected
  this afternoon and evening. Strong and possibly damaging
  winds and heavy rainfall are the primary concerns, though
  large hail is still possible.

- A Flash Flood Watch has been issued for the South Fork burn
  scar area due to the potential for multiple rounds of
  thunderstorms with heavy rainfall in the vicinity.

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

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 217 PM MDT Thu Jun 25 2026

Tonight...Severe Thunderstorm Watch in effect until 8 PM MDT for all
southeast Wyoming counties. WSR-88D and visible satellite imagery
show a healthy cluster of thunderstorms forming just northwest of
our forecast area in western and central Wyoming. Models have
consistently shown a northeast to southwest oriented line of showers
and thunderstorms affecting Carbon and Converse Counties late this
afternoon, with the line of storms propagating southeastward through
the evening across our counties.

Impressive 850-700 mb and 700-500 mb theta e ridge axis resides in
the clearing ahead of the line and shortwave trough approaching will
help ignite a nearly unbroken line of thunderstorms. HRRR has
consistently shown this well, and thus we have high POPS timed well
thanks to coordination between our midnight and day shift
Meteorologists. Main threats from the thunderstorms will be strong
outflow and straight line winds, with hail and locally heavy rain as
a secondary threat.

After the line of thunderstorms passes, widespread low clouds and
fog will develop east of I-25 again in the moist upslope flow.

Friday...One more day of possible severe thunderstorms Friday
afternoon and evening, as a healthy 850/700 mb theta-e ridge axis
forms north to south across far eastern Wyoming and the Nebraska
Panhandle. Concur with the Storm Prediction Center Marginal risk for
severe storms east of I-25 due to impressive CAPE of 2000 to 3000
J/kg, and somewhat limited bulk shear values near 35 knots.

Synoptically, a shortwave trough aloft will lie across eastern
Wyoming near peak heating, with deepening surface low pressure
across central Wyoming, and a decent low level convergence axis
developing in the afternoon from Casper to Cheyenne.

Friday night...After residual evening thunderstorms across the
Nebraska panhandle move off to our east, clearing skies and quiet
weather will ensue.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Issued at 217 PM MDT Thu Jun 25 2026

A large upper level trough will set up shop over the Pacific
Northwest at the beginning of the long term. The western lobe of
this trough is favored to have more vorticity and energy. This
vorticity lobe will swing south and north while becoming negatively
tilted as it move over our area Monday. We would typically expect
unsettled weather with such setups, however it appears the dryline
will be too far east, shutting off our access to moisture for
widespread rain.

Saturday the dryline will mix well east of the area by midday.
Following the passage of the line winds will increase from the
southwest and humidity will plummet. Minimum humidities will be at or
below 20 percent area wide with gusts to 30-45 mph. Some elevated
fire concerns could materialize from these supportive conditions.
This would impact our western counties the most, however fuels are
still green in the latest reporting. The SPC has given this area 30-
70% chances of low relative humidities and gusty winds through the
entirety of the long term. Therefore, elevated fire weather concerns
will stay with us for awhile.

There is a chance of some strong thunderstorms along the dryline as
it mixes east Saturday afternoon. The machine learning guidance is
highlight a risk in the Nebraska Panhandle regions. The current
thinking is the dryline will be too far east, but if the line does
stall more west we could see a few storms go up before leaving the
CWA quickly.

Sunday a cold front associated with the aforementioned trough will
make its way through the area. A slight uptick in precipitation
probabilities is anticipated mainly for the northern portions of the
CWA, though widespread rain is unlikely. GEFS ensemble members have
between a 40-70% of points receiving any measurable rainfall.
Following the frontal passage we stick with a dry and warming trend.
Highs creeping into the 90s west of I-25 by Thursday. Gusty winds
will continue to no ones surprise. It probably will not be until
Wednesday or Thursday that moisture makes its return to our most
eastern counties. A few dry storms could then be allowed to develop
with enough lifting from the persistent but disorganized troughing
to our west.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1126 AM MDT Thu Jun 25 2026

A weather disturbance aloft, also known as a shortwave trough
aloft, will move across the terminals late this afternoon,
through this evening, producing a line of showers and
thunderstorms that will likely produce wind gusts in excess of
50 mph along the line. Before that, expect widespread showers
and a few thunderstorms. After the line of showers and
thunderstorms moves through, widespread areas of low clouds and
fog will develop for Cheyenne, Chadron, Alliance, Scottsbluff
and Sidney for late tonight into early Friday morning.

Wyoming TAFS...For Rawlins and Laramie, high confidence for VFR
prevailing, with scattered thunderstorms from 21Z to 03Z,
producing wind gusts of 25 to 35 knots. Occasional MVFR in
showers and thunderstorms.

For Cheyenne, high confidence in VFR prevailing, with occasional
MVFR through mid afternoon in scattered showers and isolated
thunderstorms. High confidence in scattered showers and
thunderstorms along a line from 00Z to 02Z, producing wind gusts
to 45 knots, and IFR visibilities.

Nebraska TAFS...High confidence in IFR and MVFR prevailing until
mid morning Friday. Expect scattered showers and thunderstorms
along a line between 01Z and 05Z, producing wind gusts in excess
of 45 knots along with localized MVFR ceilings and visibilities.
Widespread IFR due to ceiling and visibility restrictions late
tonight until mid morning Friday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...Flash Flood Watch until midnight MDT tonight for NEZ002-095.

&&

SHORT TERM...RUBIN
LONG TERM...RV
AVIATION...RUBIN