017
FXUS65 KRIW 250401
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1001 PM MDT Fri Jul 24 2026

.KEY MESSAGES...

- Monsoon moisture continues to draw into western WY this
  evening, with isolated showers and thunderstorms expected
  mainly over west-central WY.

- This pattern continues through the weekend, with very hot
  temperatures in the 90s to near 100 degrees. Shower and
  thunderstorm chances continue for the western mountains each
  afternoon, with Saturday having the highest chances.

- Very warm temperatures with afternoon showers and
  thunderstorms continues through Thursday, with even warmer yet
  drier conditions expected for next Friday and Saturday.

&&

.UPDATE...
Issued at 1230 PM MDT Fri Jul 24 2026

As the upper-level ridge axis slowly slides west to east across
Wyoming today, temperatures are climbing compared to Thursday,
with afternoon high temperatures ranging from the upper 80s to
near 100 in the lower elevations. A weak shortwave trough is
moving from NE Nevada into SE Idaho, across NW Wyoming and into
south-central MT. This feature will bring isolated showers and
thunderstorms to western Wyoming (from SW to NW) this afternoon
and evening, mainly focusing on west-central Wyoming. Some very
isolated showers and thunderstorms may push past the crests of
the Wind Rivers and Absarokas into the eastern slides of the
Wind River and Bighorn River Basins. Late this morning, the
Storm Prediction Center included a Marginal risk of severe
thunderstorms from NW Nevada into SE Idaho, indicating the
threat of 60-70 mph wind gusts. The edge of the marginal is
right along the ID/WY border, so west-central Wyoming (Star
Valley, etc.) may see wind gusts of 50+ mph with storms this
afternoon. Elsewhere, the storms should bring brief heavy rain
and gusty outflow winds of 30-50 mph. A few showers should
linger until midnight or so before dissipating.

The ridge axis centers over the eastern Wyoming border on
Saturday, bringing in slightly warmer mid-level air along with
increasing southwest flow. A stronger shortwave trough from the
Great Basin will again move through western Wyoming into
southern Montana. More widespread isolated to scattered showers
and thunderstorms are expected Saturday, even though afternoon
high temperatures in the lower elevations will range from the
low 90s to over 100 degrees. West-southwest winds will increase
to 10-15 mph in the afternoon, with gusty outflow winds of 30-50
mph possible as well. A higher chance of 40-60 mph thunderstorm
outflow winds will be over the northern Bighorn Basin with the
thunderstorms in the late afternoon. Showers and isolated
thunderstorms will linger into the late evening as winds
decrease.

Sunday looks to be a repeat of Friday, with only isolated
showers and thunderstorms, expect that the afternoon high
temperatures will be similar to Saturday. As a result, a Heat
Advisory is in effect for the lower elevations east of the
Continental Divide addressing/highlighting the very warm to hot
temperatures (with elevated humidity leading to abnormally warm
minimum temperatures).

&&

.DISCUSSION...
Issued at 300 AM MDT Fri Jul 24 2026

H5 ridging begins to build across the Southern Rockies today,
reintroducing heat to the region. Temperatures today will reach
the 90s for the lower elevations, with warmest readings in the
usual lower elevations of the Bighorn Basin and along the I-25
corridor. The ridge axis remains to the east, allowing the
monsoon moisture to continue to draw northward into western WY.
Daytime heating will allow another round of showers and
thunderstorms to build along the western mountain ranges. A lack
of a considerable shortwave sweeping through will keep any
significant organization of storms from occurring, with showers
remaining more isolated in nature. The lighter steering flow
around the ridge will allow showers to move off to the northeast
from mountain ranges, but once they detach from the range, they
will generally decrease and dissipate. With slightly lower
moisture levels and enough steering flow to move any storms,
will not need to continue any Flash Flood Watches for the day
today. Once daytime heating decreases, showers will quickly
dissipate, with mostly clear skies overnight.

Saturday will see the heat ridge strengthen slightly, bringing
highs well into the 90s, with readings above 100 for the Bighorn
Basin and Johnson County. There is a very weak shortwave noted
in models, which may be enough to bring a little more
organization to western showers and thunderstorms, but will they
be able to overcome capping from the increased ridging is the
question. Right now, shower activity looks to be more
widespread, but showers would be smaller in nature, and would
have better motion to keep from sitting in one place.

Longer range models don`t have much change in this pattern for
the upcoming week. High temperatures hover in the 90s each
afternoon, while the chance for monsoon showers continues for
the western mountains. Shower activity would be more dependent
on any passing shortwaves enhancing any lift.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1000 PM MDT Fri Jul 24 2026

VFR conditions will be the norm over the next 24 hours. Isolated
showers will be possible over southwestern portions of the state
through 12Z this morning, however confidence remains below 20%
for these showers to directly impact KBPI/KPNA. Otherwise
expect dry conditions through the rest of the night.

Chances for showers and thunderstorms return Saturday afternoon,
with PROB30 groups for all terminals starting around 20Z/21Z.
Confidence is highest with wind being the main threat, although
IFR visibilities due to heavy rain remain a possibility is a
storm were to move directly over the terminal. Future forecasts
may change slightly, as model trends have decreased the areal
coverage for the storms Saturday afternoon. KRKS could be the
one site that remains under threat.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC
for the latest information on smoke, icing and turbulence
forecasts.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon Saturday to 9 PM MDT Sunday for
WYZ003>006-010-011-017-018-020.

&&

$$

UPDATE...McDonald/Wittmann
DISCUSSION...Straub
AVIATION...VandenBoogart/LaVoie