855
FXUS65 KRIW 250208
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
808 PM MDT Sun Aug 24 2025

.KEY MESSAGES...

- Hazy conditions and poor air quality will continue this
  evening for parts of Star Valley, the Upper Green River Basin,
  and the Wind River Basin.

- Scattered showers continue across southwestern Wyoming
  tonight, with more storms tomorrow afternoon.

- A wetter and cooler pattern develops for much of the upcoming
  week with daily chances for showers and thunderstorms. Heavy
  rain will become an increasing threat heading into this week
  as well.

&&

.UPDATE...
Issued at 1230 PM MDT Sun Aug 24 2025

Wildfires continue to burn with smoke lingering from the Dollar Lake
and Willow Creek Fires. Locations such as Star Valley, the Upper
Green River Basin and even the Wind River Basin may see periods of
hazy skies and poor air quality as the fires plume up throughout the
day today.

Not much has changed in regards to the forecast for the upcoming
week. Scattered showers and thunderstorms still are expected to
develop this afternoon and evening. The best chances for
precipitation remains across western and southern Wyoming.
Temperatures are still expected to remain around seasonable today
with highs in the low to mid 80s. Cooler temperatures arrive by
the middle of the week with highs in the upper 60s to lower 70s
west of the Divide and upper 70s east of the Divide. Along with
the cooler temperatures will come increased monsoonal moisture
which will bring increased daily chances for showers and
thunderstorms. Above normal PWATs persist across the region for
much of the week. The best chances of showers and thunderstorms
throughout much of the upcoming week remains over western and
southern Wyoming. Chances for showers and thunderstorms east of
the Divide increase later in the week. Long range models still
remain uncertain in regards to how quickly moisture flow will be
cut off for the end of the week into the weekend.

&&

.DISCUSSION...
Issued at 225 AM MDT Sun Aug 24 2025

The weather is mainly quiet across the area covered by the humble
Riverton weather abode. We only have a few virga showers at this
time. This will not last though, as precipitation chances will
be on the upswing as we head into the next week.

Monsoonal moisture will be on the increase from the south today.
However, the models trend to rush it in by around a day. In
addition, it usually comes in aloft at first in the mid and high
levels. So, although there will be an increased coverage of storms,
with the best chance across southern Wyoming (as much as a 2 in
5 chance later this afternoon), we kept QPF under a tenth of an
inch for the most part. If there is a spot that could get more,
it looks to be far southwestern Wyoming where the moisture will
deepen the fastest. Chances generally taper east of the Divide,
where the chance is 1 out of 5 at most with most areas seeing
nothing. Temperatures should run close to normal and fairly
close to yesterday`s highs. Storms should decrease tonight, but
some showers may linger through the night.

Coverage of showers and storms, and the chance of rain, possibly
excessive then really increases starting Monday as the moisture
layer begins to deepen. Reasoning on the timing remains fairly
similar to yesterday`s forecast. For Monday and Tuesday, the
most numerous storms look to be largely west of the Continental
Divide, with precipitable water values rising as high as 150 to
175 percent above climatological normals. In areas east of the
Divide, values remain near to below normal on Monday before
increasing on Tuesday as moisture begins spreading eastward.
The most numerous showers and storms still look to be on
Wednesday and Thursday as the core of the moisture moves over
the area. At this point, which day is the wettest is still in
question as there is still some spread. Most guidance agrees on
Wednesday being wet, with some areas seeing precipitable water
values climbing as high as 200 percent of normal, possibly
increasing the chance of localized flooding. There is more
spread on Thursday as some guidance, especially the GFS, is
showing drier air pushing in as flow turns more westerly as
opposed to southerly, dropping precipitable water values back to
near normal levels. This has not been consistent though and I
am not buying it yet. Most guidance then shows a drying trend
starting Friday and into next weekend as ridging slowly builds
across the Northern Rockies.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 413 PM MDT Sun Aug 24 2025

VFR conditions are expected to prevail through the period at all
terminals. Winds remain light (10 kt or less) for all terminals
as well. Monsoonal moisture continues to spread across the west
and south this evening, with 20 to 40% chances of showers and
thunderstorms across much of southwest WY through 02Z to 04Z.
The moisture is also starting to spread east of the Divide, so
have kept the PROB30 group at KLND with 10 to 15% chances. KRIW
could see a brief shower as well. Any of the showers and storms
are capable of producing outflow winds 25 to 35 kt, which will
remain the primary impact. Chances decrease overnight, though
mostly cloudy skies and occasional showers will linger around
KRKS through much of the period. Monsoonal moisture becomes more
widespread Monday afternoon, with most terminals seeing chances
for showers and storms. Have continued with VCSH and/or PROB30
groups to cover most likely timing of shower and thunderstorm
activity Monday afternoon.

Winds become mostly light and variable, less than 5 kt,
overnight through the end of the period. There is a slight
chance (15%) of low clouds (possible MVFR cigs) moving into KCPR
briefly towards sunrise, so have kept hints of this in the TAF,
though westward coverage of the low clouds does not look as
extensive as it was this morning.

Several active wildfires will continue across portions of western WY
and other parts of the western US, which are expected to again plume
out this afternoon. Continued occasional smoke impacts to visibility
are possible, most notably at KBPI and KPNA through the period.

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

&&

$$

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