946
FXUS65 KRIW 301120
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
520 AM MDT Sat Aug 30 2025

.KEY MESSAGES...

- Scattered showers and isolated storms will be ending later
  this morning across central portions of the CWA.

- Shower and thunderstorm chances again Saturday afternoon. The
  greatest chances (50%-70%) are across Johnson County,
  including the east slopes of the Bighorns.

- A drier trend Sunday through Tuesday of next week.
  Temperatures will be quite pleasant with highs in the upper
  70s to upper 80s. A cold front could bring highs down to the
  60s and 70s on Wednesday and Thursday.

&&

.DISCUSSION...
Issued at 118 AM MDT Sat Aug 30 2025

Synopsis...Precipitation is expected once again today, with drier
conditions returning Sunday. An upper level ridge will build over
the Great Basin into the Northern Rockies today, helping to push the
moist airmass that has been in place this week out of the area. The
Cowboy State will then be sandwiched between this ridge and a strong
longwave trough. This trough will encompass much of the eastern half
of the CONUS, including the Great Plains. As such, the forecast for
the middle of next week could become highly variable in the next few
days as models come into better agreement. At this point, it is
looking like a tale of two Divides where it will be warm with
chances for precipitation west of the Divide and seasonal and dry
east of the Divide Wednesday and Thursday.

Discussion...Showers and embedded thunderstorms over southern
portions of the Bighorn Basin into the Wind River Basin will
continue to move toward the southeast through the rest of the
morning, ending as they move into western and southern portions of
Natrona County after sunrise. Lightning will be the main threat.

Showers and thunderstorms are expected once again today, with
Johnson and Natrona counties having the better chances. This will be
due to a remnant low that continues to linger over the Black Hills
region. There is a possibility for brief heavy rain occurring
with storms over the east slopes of the Bighorns this
afternoon. Additional showers and thunderstorms will develop off
the east slopes of the Absaroka and Wind River Mountains and
move over the Bighorn and Wind River Basins into the evening.
Precipitation is expected to end across the area by midnight.
Otherwise, temperatures will be seasonal today and winds
relatively light. Gusts up to 25 mph will be possible through
the afternoon.

Conditions are expected to be mostly dry through Tuesday, with
temperatures ranging from the upper 70s to upper 80s. A cold front
looks to move across areas east of the Divide by Wednesday. Models
are in disagreement on timing and strength, with the GFS being the
(typically) faster solution and bringing it through Tuesday night.
The ECMWF has had more run-to-run consistency and brings it through
on Wednesday. Additionally, it is the more colder solution and drops
700mb temperatures to 0C to 2C. Consequently, the main storm system
will bring cold and windy conditions across the Northern Plains and
the Upper Midwest from Tuesday night into Friday (at least). The
influence of the ridge to our west will determine how much of this
system will impact the CWA. This ridge will eventually move over the
region Thursday and Friday, as that storm system moves over eastern
portions of the CONUS and Canada.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 515 AM MDT Sat Aug 30 2025

Prevailing VFR conditions will continue through the TAF period.
There are a couple of areas of showers and embedded thunder, and
these will mainly impact KWRl and KCPR through around 1400.
Patchy fog may develop in vicinity of KLND and KRIW with last
nights rain but not enough confidence to include it at this
time.

This area of showers and storms will end this morning, with
more convective development Saturday afternoon. The best chance
for impacts from convection will be at KCPR Saturday afternoon,
which is denoted by a PROB30. With the models trending a bit
wetter, we have also added PROB30 groups after 18Z in vicinity
of KWRL, KRIW and KLND, where there is around a 1 in 4 chance of
a shower or thunderstorm through around 01Z Sunday. Wind will
remain below 10 knots, outside of convective activity, tonight
through Saturday morning. Gusty wind will develop at KBPI, KPNA,
and KRKS Saturday afternoon. Dry weather should return after 03Z
Sunday.

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


&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...LaVoie
AVIATION...Hattings