Severe Thunderstorm Warning 247, NWS Cheyenne, WY

Area Forecast Discussion
National Weather Service Cheyenne WY
219 PM MDT Sat Aug 15 2026

.KEY MESSAGES...

- Another round of thunderstorms will bring the potential for
  localized flash flooding and isolated strong to severe
  thunderstorms this afternoon and evening.

- A Flood Watch & Severe Thunderstorm Watch are in effect
  through this evening for much of the High Plains.

- Isolated strong to severe storms and localized flash flooding
  will remain possible Sunday, though overall storm coverage
  will be lower.

- Drier weather and temperatures close to seasonal averages will
  return early next week.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 216 PM MDT Sat Aug 15 2026

Another round of slow moving thunderstorms is in store for this
afternoon and evening. Looking at Water Vapor, the mid and lower
levels show plumes of moisture advecting through Colorado and
Arizona and into our region. This will drive our PWAT values into
the 1.0-1.25 inch range during the weekend as we are in Southwest
flow. 700mb flow will remain rather slow today, with generally
westerly to southwesterly flow expected. A messy, surface high
pressure system will attempt to develop west of the Rocky Mountains
over western Colorado before strengthening into the afternoon hours.
With ample moisture available due to continued monsoonal moisture
advection, the easterly flow will lead to very moist, upslope flow
along and east of the Laramie Range. 700mb and 500mb vorticity
maxima will be the major players in the synoptic forcing which is
expected to increase into the later afternoon hours. Heavy rainfall
is anticipated once again today, with the Weather Prediction Center
placing portions of the region in a Slight Risk of excessive
rainfall and a larger portion in a Marginal Risk of excessive
rainfall. With the sustained rainfall across the lower elevations
yesterday, the soils should be moderately saturated to aid in
localized areal and urban flooding. A Flood Watch was issued on the
overnight shift that is valid from 2PM through 10PM for nearly all
locations along and east of the Laramie Range, where Precipitable
Water values remain at and above the 90th percentile and moist,
upslope flow persists. In addition to the flooding risk today, the
Storm Prediction Center has placed far southeast Wyoming and western
Nebraska in a Slight Risk (Level 2 of 5) of severe weather this
afternoon. Primary hazards look to be isolated, large hail and
damaging wind gusts. Isolated pockets of MLCAPE and SBCAPE around
1000 J/kg will provide enough instability for stronger updrafts to
develop this afternoon, especially across western Nebraska. The
biggest question will be whether or not the early morning cloud
cover anticipated across the region puts a damper on the severe
potential this afternoon. Pockets of clearing skies occurred across
the forecast area to aide in some diurnal heating this morning and
strengthening the instability for the showers/thunderstorms later.
Forecasting the daily high temperatures and trying to get the hourly
trend will be rather difficult as these clouds push into the region
potentially cooling areas faster than the models could predict as
well.

For Sunday, slightly drier condition as the upper-level flow turns a
little more westerly, cutting off some of the monsoonal moisture
advection into the area. However, with the ample moisture present
over the past several days, plenty of residual moisture will be
present to get another round of showers and storms Sunday afternoon
into the evening hours. A few lobes of 500mb vorticity will advect
across the region Sunday afternoon, providing some forcing for
ascent. Slightly stronger 700mb warm air advection briefly develops
Sunday afternoon, adding an additional forcing for ascent for
showers and storms. Surface flow turns southerly Sunday afternoon
through much of the overnight hours, leading to weak ascent across
the Cheyenne Ridge, likely resulting in showers and storms
developing in this area once again. Precipitable water values look
to return towards more climatologically average values Sunday,
decreasing the threat for isolated flooding across the region.
However, with monsoonal moisture still in play, flooding potential
continues for Sunday with a Marginal Risk of Excessive Rainfall from
the Weather Prediction Center. Another round of strong to severe
storms will be possible Sunday, with a Slight Risk of severe weather
for much of the area and a small portion of the region under a
Slight Risk of severe weather once again.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Issued at 216 PM MDT Sat Aug 15 2026

Drier air will work into the area on Monday, bringing us a break in
the stormy monsoon weather pattern. Expect mostly sunny skies to
return to the area with temperatures generally near seasonal
averages, in the lower 80s around Laramie and Rawlins, and mid to
upper 80s along and east of I-25. While isolated showers and/or
thunderstorms will still be possible, coverage will be significantly
lower than the preceding days. The boundary layer will be much
drier on the Wyoming side, which may lead to a dry microburst,
threat, while a few actual rain producing thunderstorms will be
possible mainly on the Nebraska side.

The monsoon tap recovers somewhat on Tuesday into Wednesday, though
the flow will remain largely westerly aloft. Still, some low to mid
level southerly flow over the Great Basin will help inject higher PW
into our area, pushing values back to around 0.75 and 1.2 inches or
so across the area. This will of course be not quite as high as the
current monsoon surge, but should be sufficient to kick up coverage
of showers and thunderstorms for Tuesday and Wednesday, especially
with some help from an upper level shortwave trough riding over the
top of the ridge Wednesday. While the boundary layer will still b on
the dry side during this period, there looks to be plenty of
moisture aloft so rain should still reach the ground even in the
drier areas. Tuesday should see temperatures climb just a smidge
above seasonal averages, while these values will fall by a few
degrees Wednesday with the aforementioned shortwave.

The upper level ridge will amplify to our west on Thursday, and
Friday, turning the flow aloft to a more dry, northwesterly flow.
Expect storm chances to become much more isolated once again as
temperatures climb back above seasonal averages. An early look at
700-mb temperatures appears fairly marginal for record highs
with this round with NAEFS means hovering around +15 to +18C, or
near the climatological 90th percentile.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1142 AM MDT Sat Aug 15 2026

Thunderstorms and heavy rainfall will be the main aviation
concern once again today. Storms will kick up in the next 1-2
hours in southeast Wyoming, impacting KLAR and KCYS in the
afternoon, then progressing eastward into the Nebraska panhandle
in the late afternoon and evening hours. Strong, gusty outflow
winds and IFR conditions due to moderate to heavy rainfall will
be the primary concerns. TEMPO groups were introduced where
confidence in impacts is highest, while other terminals remain
at PROB30 groups. Timing is still a little uncertain, so be
alert for possible AMDs this afternoon and evening as confidence
increases.

Look for largely variable winds overnight behind today's
thunderstorm activity. Another round of low clouds and/or fog is
possible over the High Plains, but confidence is fairly low.
Model probabilities are around 20 to 30% for MVFR to IFR, but
models have been underestimating the fog and low CIGs the last
several mornings.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Flood Watch until 10 PM MDT this evening for WYZ102-107-108-
     117>119.
NE...Flood Watch until 10 PM MDT this evening for NEZ002-003-
     019>021-054-055-095-096.

&&

SHORT TERM...MM
LONG TERM...MN
AVIATION...MN

Special Weather Statement
National Weather Service Cheyenne WY
328 PM MDT Sat Aug 15 2026

WYZ101-152200-
Converse County Lower Elevations WY-
328 PM MDT Sat Aug 15 2026

...A STRONG THUNDERSTORM WILL IMPACT CENTRAL CONVERSE COUNTY THROUGH
400 PM MDT...

At 327 PM MDT, Doppler radar was tracking a strong thunderstorm 11
miles northwest of Fort Fetterman Historic Site, or 18 miles
northwest of Douglas, moving east at 30 mph.

HAZARD...Wind gusts of 50 to 55 mph and nickel size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor hail damage to vegetation is
         possible.

Locations impacted include...
Douglas, Converse County Airport, and Fort Fetterman Historic Site.

This includes Interstate 25 in Wyoming between mile markers 137 and
143.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4296 10570 4305 10567 4313 10520 4271 10538
TIME...MOT...LOC 2127Z 279DEG 26KT 4299 10559

MAX HAIL SIZE...0.88 IN
MAX WIND GUST...55 MPH

Brauer

Special Weather Statement
National Weather Service Cheyenne WY
329 PM MDT Sat Aug 15 2026

WYZ103-106-152200-
Central Laramie Range and Southwest Platte County WY-
North Laramie Range WY-
329 PM MDT Sat Aug 15 2026

...A STRONG THUNDERSTORM WILL IMPACT EAST CENTRAL ALBANY AND WEST
CENTRAL PLATTE COUNTIES THROUGH 400 PM MDT...

At 329 PM MDT, Doppler radar was tracking a strong thunderstorm 9
miles northwest of Flying X Ranch, or 24 miles west of Wheatland,
moving northeast at 25 mph.

HAZARD...Wind gusts of 50 to 55 mph and half inch hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor hail damage to vegetation is
         possible.

This storm will remain over mainly rural areas of east central Albany
and west central Platte Counties.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

A Severe Thunderstorm Watch remains in effect until 900 PM MDT for
southeastern Wyoming.

&&

LAT...LON 4192 10546 4202 10555 4222 10529 4191 10506
TIME...MOT...LOC 2129Z 236DEG 23KT 4199 10544

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...55 MPH

Brauer

Special Weather Statement
National Weather Service Cheyenne WY
337 PM MDT Sat Aug 15 2026

NEZ002-003-152215-
Box Butte NE-Dawes NE-
337 PM MDT Sat Aug 15 2026

...A STRONG THUNDERSTORM WILL IMPACT NORTHEASTERN BOX BUTTE AND
SOUTHEASTERN DAWES COUNTIES THROUGH 415 PM MDT...

At 337 PM MDT, Doppler radar was tracking a strong thunderstorm 7
miles south of Roberts Trailhead Campground, or 19 miles southwest of
Chadron, moving east at 25 mph.

HAZARD...Wind gusts of 50 to 55 mph and penny size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor hail damage to vegetation is
         possible.

Locations impacted include...
Box Butte Reservoir, Box Butte Campground, and Box Butte Dam.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

A Severe Thunderstorm Watch remains in effect until 900 PM MDT for
the Panhandle of Nebraska.

&&

LAT...LON 4254 10324 4264 10320 4265 10279 4238 10298
TIME...MOT...LOC 2137Z 284DEG 22KT 4257 10315

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...55 MPH

Brauer

Special Weather Statement
National Weather Service Cheyenne WY
358 PM MDT Sat Aug 15 2026

WYZ101-103-152230-
Converse County Lower Elevations WY-North Laramie Range WY-
358 PM MDT Sat Aug 15 2026

...A STRONG THUNDERSTORM WILL IMPACT WEST CENTRAL CONVERSE COUNTY
THROUGH 430 PM MDT...

At 358 PM MDT, Doppler radar was tracking a strong thunderstorm near
Deer Creek, or 23 miles west of Douglas, moving east at 15 mph.

HAZARD...Wind gusts of 50 to 55 mph and half inch hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor hail damage to vegetation is
         possible.

Locations impacted include...
Glenrock, Deer Creek, and Laprele Reservoir.

This includes Interstate 25 in Wyoming between mile markers 153 and
165.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

&&

LAT...LON 4273 10590 4281 10594 4294 10571 4265 10555
TIME...MOT...LOC 2158Z 257DEG 13KT 4277 10585

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...55 MPH

Brauer

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