364
FXUS65 KRIW 222300
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
500 PM MDT Fri Aug 22 2025

.KEY MESSAGES...

- Slightly stronger wind from the north behind a reinforcing
  cold front this afternoon into tonight.

- Rain chances will be very isolated until Sunday, with dry lightning
  a distinct possibility each afternoon.

- A monsoonal type pattern will develop late this weekend into
  early next week, which will provide chances for rain showers
  and thunderstorms each day beginning Sunday, mainly across
  southwest Wyoming.

- The increased moisture will also lead to increased cloud cover
  and overall much cooler temperatures next week.

&&

.UPDATE...
Issued at 1104 AM MDT Fri Aug 22 2025

Skies have mostly cleared this morning, which will allow for surface
heating to increase instability heading into the afternoon hours.
Model guidance is holding off most of the convection until just
before sunset, with lingering convective activity into tonight. This
makes sense as the subtle shortwave compresses the high a little
more by that time and provides more lift from the right entrance
region of the jet. Air quality has improved for the Bighorn Basin
today as the Red Canyon Fire did not produce much smoke yesterday.
Unfortunately, another large fire, the Dollar Lake Fire, developed
in the northern Wind River Mountains near the Green River Lakes
yesterday. This fire is producing plenty of smoke as it is burning
in a densely forested area. This has resulted in the issuance of an
Air Quality Alert for the Upper Green River Basin and the western
Wind River Mountains, but smoke will also stream over the Wind River
Basin this afternoon.

Gusty and erratic outflow wind may cause problems for active
wildfires this afternoon and evening, even though RH is above
critical levels. Dry lightning may cause new fire starts again,
today. With monsoonal moisture expected next week there will remain
the threat of dry lightning and gusty outflows around the periphery
of the moisture in central and northeastern portions of the area.
How high of a threat will depend on the northeastern extent of the
low-level moisture values advecting into Wyoming.

&&

.DISCUSSION...
Issued at 158 AM MDT Fri Aug 22 2025

Today`s forecast looks similar to yesterday. The area will be in
between an upper-level low centered in Canada and an upper-level
high centered around the Four Corners area. Northwest flow aloft
keeps the cooler temperatures from yesterday in place, especially
east of the Continental Divide, where the trough`s influence is
greater. Highs today are in the mid-80s for most locations, with the
cooler areas being around Johnson County where the highs are in the
mid-70s.

The moisture from yesterday also continues today, with afternoon and
evening showers and thunderstorms possible. Though an isolated (10%
or greater) shower or storm is possible anywhere, the best chances
(20%-60%) occur from an Afton to Cody line and east. Hi-res models
are in best agreement for storms across Sweetwater County, northeast
into southern Johnson County (which includes southeast Fremont
County and Natrona County). This area is also where the best chances
for stronger storms would be, including gusty outflow winds and
small hail. Gusts 30 to 40 mph would be most common with the
stronger storms, though isolated gusts to around 50 mph are
possible. Showers and storms will linger late, possibly to around
sunrise Saturday morning.

For Saturday, the upper level pattern has the high shift westwards.
This will temporarily limit moisture into the area, so chances for
showers and thunderstorms greatly decreases. There will likely still
be a few that pop-up during the afternoon, but would be limited in
coverage and favored to initiate over the mountains. Sunday,
moisture rotating around the high makes it to the area, with shower
and storms chances increasing again. Coverage of rain chances
increases further Monday as monsoonal moisture makes it to the area.
The chances for wetter showers and storms therefore also increases
for Monday. This wetter and cooler pattern looks to continue through
next week. Though too early to accurately forecast liquid amounts for
next week, the pattern would favor higher amounts west of the
Divide, with the EFI/SOT highlighting southern and southwestern
Wyoming for higher than climatological liquid amounts (QPF).

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 500 PM MDT Fri Aug 22 2025

A smoke plume from the Dollar Lake Fire in far northern Sublette
County continues to stream over Fremont County and into Natrona
County. No vis restrictions from the smoke are expected at
these terminals through the period, however there will be
mountain obscurations over the Wind River Mountains near the
fire. Otherwise, expect hazy skies over Fremont and Natrona
counties through the day Saturday.

Isolated showers and thunderstorms will continue over central
and southern portions of the forecast area. The bulk of this
activity looks to stay together and move toward KCPR and
southern Natrona County between 04Z and 08Z. There remains
enough confidence to continue a PROB30 group at KRKS between 00Z
and 04Z. Isolated strong gusty outflow winds of 20 to 30 kt
will be possible from this convective activity. Lowered cloud
ceilings, FL050-080, will develop at KCPR, KRIW/KLND by 06Z.
Lower ceilings of 2000 to 3500 ft cannot be ruled out at KCPR,
but confidence remains too low to include in the forecast at
this time. Clouds will scatter out through the morning after
sunrise, with SKC skies in place across much of the area by 18Z.

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...Rowe
DISCUSSION...Wittmann
AVIATION...Dziewaltowski/LaVoie