128
FXUS65 KRIW 231537
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
937 AM MDT Sat Aug 23 2025

.KEY MESSAGES...

- Wildfire smoke is expected to linger through the weekend
  across portions of the Upper Green River Basin, Star Valley,
  and Bighorn Basin leading to hazy conditions and poor air
  quality.

- An isolated shower or thunderstorm is possible this afternoon
  and evening mainly in the higher elevations.

- Chances of showers and thunderstorms increase again on Sunday
  as monsoonal moisture surges back into the area.

- Much of next week will have daily chances of showers and
  thunderstorms, with the middle of the week having the best
  chance. Much needed rain is likely for many areas for this
  period.

&&

.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 though 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 /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 504 AM MDT Sat Aug 23 2025

VFR conditions prevail through the period. Outside very
isolated showers near mountains this afternoon, no precipitation
is expected to impact any sites today. Smoke from wildfires
will be present, mainly impacting Fremont, Natrona, and Sublette
Counties.


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.

&&

$$

DISCUSSION...Hattings
AVIATION...Wittmann