845
FXUS65 KRIW 071115
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
515 AM MDT Mon Sep 7 2026

.KEY MESSAGES...

- Rain showers will end across the area after sunrise this
  morning. Conditions will be cooler, with winds increasing
  through the morning. Widespread gusts of 30 to 45 mph will
  occur through the afternoon.

- Near-critical to critical fire weather conditions return. A
  Red Flag Warning is in effect for portions of the Bighorn
  Basin this afternoon.

- Wind and low humidity will lead to continued fire weather
  concerns through the rest of the week. A storm system
  continues to trend toward cooler and wetter conditions next
  weekend.

&&

.DISCUSSION...
Issued at 235 AM MDT Mon Sep 7 2026

Showers continue to subside over the northern half of the
forecast area early this morning, with isolated thunderstorms
over far western portions. This precipitation will end across
the area by 15Z this morning as winds begin to increase. A dry
slot will be in place over the Cowboy State by this time, with
the main sfc low in the vicinity of MT/ND and the associated
occluded low over western MT. West-southwest winds, with gusts
of 25 to 35 mph will be in place from Kemmerer to Casper by this
time. Higher winds of 30 to 45 mph will occur over portions of
YNP and the east slopes of the Absaroka, Bighorn and Wind River
Mountains. Winds will continue to increase across the forecast
area, with gusts of 25 to 40 mph occurring for most areas by
18Z. Fire weather will once again be a concern as a result, with
near- critical RH values returning. This will be especially
true east of the Divide, where critical RHs will be in place in
the Bighorn Basin. A Red Flag Warning is in effect for Big Horn,
Washakie and Hot Springs counties this afternoon as a result. A
cold front will move eastward through the afternoon, exiting
the CWA into southeast WY between 06Z and 09Z Tuesday. Winds
will subside through the evening, becoming light for much of the
area after midnight. Freezing temperatures will be possible in
the western valleys and portions of the Upper Green River Basin
Tuesday morning in the wake of the cold front.

More seasonal temperatures and dry conditions will remain in
place Tuesday, with freezing temperatures possible again in the
western valleys and Upper Green River Basin Tuesday
night/Wednesday morning. Needless to say, sub-freezing
temperatures will be in place in the higher elevations the next
two nights. Fire weather will be the main concern through the
rest of the week. West-southwest winds, with gusts of 25 to 35
mph, will occur each afternoon with slightly stronger gusts
possible Thursday and Friday. Critical RHs will be widespread
east of the Divide Tuesday, spreading across southern portions
Wednesday. An extended period of Red Flag Warnings looks likely.

Models continue to trend toward a strong cold front impacting
the Cowboy State next weekend. The GFS continues to be the most
aggressive, digging a Canadian low southward to northern
portions of the Great Basin and spreading widespread
precipitation over the state ahead of it. The ECMWF is slower
and not as progressive, keeping the system over the Northern
Rockies and moving over the region Sunday into Monday next week.
Although the timing remains influx, this continues to trend
toward the first taste of autumn to the region.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 508 AM MDT Mon Sep 7 2026

A line of showers and embedded thunderstorms continues over far
western WY this morning. Precipitation is expected to end across
the area by 15Z, with SKC skies through the rest of the period.
Winds will increase across much of the area by this time, with
gusts of 25 to 30kt occurring at every terminal by 18Z. These
winds will gradually decrease after 00Z, becoming light (11kt or
less) by 03Z.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

.FIRE WEATHER...
Issued at 235 AM MDT Mon Sep 7 2026

Rain showers will end across the area by 0900 this morning, with
conditions remaining dry through the rest of the day. Winds
will increase across the area during this time with gusts up to
30 mph already occurring from Kemmerer to Casper. Higher gusts
of 35 to 45 mph are expected in the mountains and northwestern
portions by 0900 as well. Winds will continue to increase across
the area through the rest of the morning, with gusts of 30 to
40 mph occurring for most locations by 1200. Critical RHs will
be confined to zones 275/282 this afternoon, but other areas
east of the Divide will have RHs ranging between 16 and 20%. A
cold front will push into northern portions of the Bighorn Basin
between 1300 and 1500, progressing to the south and east
through the afternoon reaching Greybull/Basin by 1800. The front
will pass through the rest of the Bighorn Basin by 2100 as winds
decrease across the area.

Red Flag conditions are likely through the rest of the week,
with multi-day Red Flag Warnings expected.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon today to 7 PM MDT this evening for
WYZ275-282.

&&

$$

DISCUSSION...LaVoie
AVIATION...LaVoie
FIRE WEATHER...LaVoie