118
FXUS65 KRIW 241831
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1231 PM MDT Sun Aug 24 2025

.KEY MESSAGES...

- Wildfire smoke may bring hazy conditions and poor air quality
  to parts of Star Valley, the Upper Green River Basin, and the
  Wind River Basin today.

- Scattered showers and thunderstorms will begin to develop
  this afternoon and evening mainly across western and southern
  Wyoming.

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

&&

.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 low 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 the southern Wyoming (as much as a 2 in
5 chance later this afternoon), we kept QPF under a tenth of an inch
for 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 remains the same. 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 spread 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 bring 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 /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1135 AM MDT Sun Aug 24 2025

VFR conditions are expected to prevail through the period at all
terminals. Winds remain light (10kts or less) for all terminals as
well. Monsoonal moisture continues to increase today, with 20 to 40%
chances of showers and thunderstorms across much of southwest WY.
Have added PROB30 groups for all sites west of the Divide (KBPI,
KPNA, KJAC, and KRKS) as well as KLND for this afternoon to cover
these chances. Showers look to begin to develop later in the
afternoon (after 20Z) with impacts lingering through the evening.
Most likely impacts today will be gusty outflow winds 25 to 35 mph.
Chances decrease overnight, though mostly cloudy skies and
occasional showers will linger around KRKS through much of the
period.

Winds become mostly light and variable, less than 5kts,
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 added 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 wildfire 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...Hensley