743
FXUS65 KRIW 020355
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
955 PM MDT Mon Sep 1 2025

.KEY MESSAGES...

- Isolated evening showers over the Absaroka Mountains and the
  northern Wyoming Range fade between 8 and 10 PM Monday.

- Tuesday sees isolated showers and even a thunderstorm or two
  develop between 1 and 3 PM over the Absaroka, Wind River, and
  Bighorn Mountains before these track southeast until sunset.
  The pattern looks similar for Wednesday afternoon and evening.

- Temperatures cool 4-8 degrees east of the Continental Divide
  Wednesday as a cold front sweeps south through that region.

- Moisture arriving from the southwest increases the chance for
  showers and thunderstorms Friday, with coverage becoming more
  widespread over the weekend.

&&

.UPDATE...
Issued at 135 PM MDT Mon Sep 1 2025

Little change to the 0-48 hour forecast today. High pressure
continues to influence the weather over western and central
Wyoming, with mostly clear skies over the lower elevations, and
partly cloudy skies over the mountains as weak to moderate
cumulus builds orographically. Some models are suggesting light
showers and a very low chance of thunderstorms over the
Bighorns, Absarokas, and Wind Rivers this afternoon. The Wyoming
Range is also another area to look out for. Temperatures remain
very near normal or just above normal, with a few degrees of
warming on Tuesday. Winds are relatively light, so even though
RH values will drop to 15% or lower from the Bighorn Basin to
the Wind River Basin and Dubois area south to Sweetwater County,
wind gusts should remain at 15 mph or lower. Tuesday looks to be
a near repeat of Monday with a few more clouds and continued
chance of afternoon showers along and east of the divide.

The biggest weather impacts for the next few days will be a
couple of cool fronts impacting areas east of the divide both
Wednesday and Thursday. Shortwave troughs are expected to move
from the MT/ND border SSE into central Nebraska both days,
draping cool fronts across central and eastern WY. Clouds are
expected to increase with a better chance of showers around the
Bighorn Mountains and from Johnson into Natrona Counties.
Temperatures will decrease with the biggest change noted on
Thursday. North winds will increase primarily during the
afternoons and evenings east of the divide. Northern Johnson
County could see 30-40 mph gusts Thursday afternoon as a result.

&&

.DISCUSSION...
Issued at 133 AM MDT Mon Sep 1 2025

Conditions will remain mostly dry today and are expected to remain
so through at least Thursday. Temperatures will be somewhat
seasonal, ranging from the upper 70s to upper 80s. Today and Tuesday
will be the warmest days, especially in the Bighorn Basin where
highs will approach the 90 degree mark. Winds will stay light,
with periods of high clouds from time to time. Elevated fire
weather conditions will also return to the central basins and
southern portions of the CWA this afternoon, as RH values become
critical in these areas. There is a 10 to 20% chance for virga
showers to develop over the Bighorn, Absaroka and Wind River
Mountains this afternoon, but these chances could go down later
today, as confidence remains low due to the overall dry
conditions. The synoptic pattern through much of the week will
be largely unchanged: the Cowboy State will be sandwiched
between an upper level ridge to the west and a strong developing
longwave trough to the east. The influence of these two
features could cause some variability for each side of the
Divide by Thursday and Friday. The smoke that moved into the
area yesterday will remain in place today, keeping skies hazy.

The anticipated cold front looks to move across areas east of the
Divide starting Wednesday morning and quickly exiting the area
to the south by early afternoon. Temperatures will be slightly
cooler as a result, but will have the biggest impact over
northern Johnson County where highs will be in the lower 70s
(about 12 degrees cooler from Tuesday). A second surge of cooler
air looks to move over the Cowboy State Friday, resulting in
highs in the 70s to near 80 degrees. The ridge will begin to
shift eastward over the state by Saturday, bringing the next
chance for widespread precipitation to the CWA. Most of this
looks to be confined to areas west of the Divide for now.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 955 PM MDT Mon Sep 1 2025

VFR conditions prevail at all terminals through the forecast period
in northwest flow aloft. The possible exceptions would be western
wildfire smoke wafting into KCOD and producing brief MVFR
visibility, and KPNA where a drainage wind may bring smoke from the
nearby Dollar Lake wildfire into the valley late tonight. There is
enough mid-level moisture to again generate isolated late day
showers and a thunderstorm or two over the Absaroka, Wind River, and
Bighorn Mountains Tuesday. Steering winds lead to a few more clouds
and the outside chance at a shower at KCOD and KRIW around
00Z/Wednesday. Any lingering convection should wane by 04Z/Wednesday.
Surface wind increases at most terminals to 7-10 kts after 21Z-
22Z/Tuesday. A better northerly surge reaches the far north just
beyond the end of this forecast period.

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...
None.

&&

$$

UPDATE...McDonald
DISCUSSION...LaVoie
AVIATION...CNJ