866
FXUS65 KRIW 232240
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
440 PM MDT Sat Aug 23 2025

.KEY MESSAGES...

- New fire starts and growing fires have created smokey
  conditions across portions of Star Valley, the Upper Green
  River Basin and the Bighorn Basin.

- An isolated shower or thunderstorm cannot be ruled out this afternoon
  mainly over higher elevations.

- Increased chances for showers and thunderstorms arrives Sunday with
  the best chances over central and southern Wyoming.

- A wetter and cooler pattern develops for the upcoming week
  with daily chances for showers and thunderstorms.

&&

.UPDATE...
Issued at 1234 PM MDT Sat Aug 23 2025

Satellite imagery shows plumes of wildfire smoke across portions of
the Cowboy State today. Interestingly enough, three different
parts of the state have smoke aloft and all three are from
different sources. A new fire start called the Willow Creek Fire
near Salt River Pass has grown and begun to produce a plume
into eastern Lincoln County and western Sweetwater County. The
Dollar Lake Fire continues to burn nearby the Green River Lakes,
bringing smoke over the Wind River Mountains and into parts of
the Upper Green River Basin and Wind River Basin. The last
location is the Bighorn Basin, where smoke from fires in Idaho
has funneled over the area. The smoke may create some poor air
quality as well as produce hazy conditions. An isolated shower
or thunderstorm cannot be ruled out this afternoon and evening,
mainly across the higher elevations of central Wyoming.

The overall forecast remains on track with little to no change
expected over the next few days. Temperatures will be near
seasonable through the weekend with highs ranging in the low to
mid 80s. Cooler temperatures arrive for most of the upcoming
week with highs slightly below normal. Many locations can expect
to see highs in the 70s, which will be a nice break from the
summer heat. Above normal PWATs begin to build in as early as
Sunday, bringing increased chances for showers and
thunderstorms during the afternoon and evening. Model guidance
remains mostly unchanged with monsoonal moisture gradually
building back into the region for the upcoming week due to
favorable southwesterly flow. The influx of moisture will lead
to daily chances for showers and thunderstorms through the week.
The best chances for precipitation will be across western and
southern Wyoming with lesser chances the farther north and east
you go. While still multiple days out there may be the potential
for some strong storms to develop over the upcoming week. The
increase in moisture and upper level flow may create favorable
dynamics for these stronger storms, so it will need to be
monitored as the weekend comes to an end. After a mainly dry and
hot start to August, change looks to be around the corner, with
a cooler and wetter end of the month likely.

&&

.DISCUSSION...
Issued at 1258 AM MDT Sat Aug 23 2025

Quite an active day for fires across the area, especially west
of the Divide. The Dollar Lake Fire had a very impressive plume
and some pyrocumulus development. It also pushed an area of
smoke across central Wyoming, including at our office where it
darkened the sky during the afternoon. Fires continue to burn
tonight. We also have a few showers and thunderstorms in eastern
portions of the area with an area of upper level divergence.
These should end for the most part by sunrise though.

Unfortunately, it looks like little rain to help out today. High
pressure will build into the area, pushing the deeper moisture out
of most of the day. There will still be enough moisture for a few
showers and thunderstorms. However, at this point, these look to be
mainly in and near the mountains with over 90 percent of the area
remaining dry. Wind should remain light to moderate and relative
humidity should remain a bit higher though, a bit of a silver
lining for the fires. A few high resolution models are showing a
few showers in the evening in central Wyoming. The chance is
only around 1 out of 10 though, so not enough confidence to
include in the official forecast.

Chances will increase tomorrow as monsoonal moisture begins to surge
northward across the area. However, like most surges, the initial
surge looks to be of the mid and high level variety, which means
little in the way of precipitation. There will be a chance across
approximately the southern two thirds of the area. Most areas should
not see anything though, with the best chance across southern
Wyoming. Chances then increase Monday into Tuesday for wetter
storms, with an emphasis across southern Wyoming where precipitable
water levels should rise to around 150 percent of normal. Chances
taper further to the north and west on these days where some areas
will have less then the climatological average of precipitable water
levels.

Most guidance shows Wednesday or Thursday as the two most active
days, with precipitable water values possibly rising as high as 200
percent of normal. The pattern favors western Wyoming, but some
could spread east of the Divide. Obviously, it is impossible to
pinpoint thunderstorms this far out, but there is a good chance
of some needed wetting rain across much of the area through the
period. The chance of convection also lingers through Friday,
although some guidance is showing some drier air possible
pushing in from the west, starting to shut off the convection.
So, to sum it up, we have a fairly high confidence in a wetter
pattern for much of next week. Details are still fairly
uncertain though.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 430 PM MDT Sat Aug 23 2025

Given prevailing drainage wind direction from the northwest, the
visibility may again drop to IFR/MVFR at KPNA between about 10Z-
16Z/Sunday. Otherwise, all other terminals to be VFR. KCPR could see
a SCT-BKN040 deck late tonight and early Sunday morning, but
confidence is not high. Mid-level moisture rotates into southwest
Wyoming early Sunday afternoon and generates scattered convection by
21Z/Sunday. The best chance for -TSRA and gusty wind appears to be
at KRKS, where PROB30 exists after 21Z/Sunday. However,
steering flow is not that favorable for convection coming off
the Uinta Mountains to track toward KRKS. KBPI and KPNA may need
to have PROB groups added late Sunday afternoon.

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...
Air Quality Alert until 1 PM MDT Monday for WYZ014-025-026.

&&

$$

UPDATE...Dziewaltowski
DISCUSSION...Hattings
AVIATION...CNJ/LaVoie