567
FXUS65 KRIW 020430
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1030 PM MDT Wed Oct 1 2025

.KEY MESSAGES...

- Warmer than average and mainly dry for Thursday and Friday
  with breezy winds giving way to some areas of elevated fire
  weather conditions.

- Confidence for widespread low elevation precipitation and high
  elevation accumulating snowfall continues to increase for
  late Friday into Saturday.

- Cold morning lows near or even below freezing may be possible
  for locations east of the Divide for the upcoming weekend
  into the start of next week.

&&

.UPDATE...
Issued at 104 PM MDT Wed Oct 1 2025

Not much to add regarding the short term forecast as things
remain mostly unchanged. Temperatures will remain warm through
Friday with colder air expected to move into the region for the
weekend into the start of next week. Isolated showers and storms
will be possible across western WY over the next few days ahead
of the next weather system. Strong gusty winds and near
elevated fire weather conditions are expected Friday. The best
chances for winds of 30 or more mph will be along the wind
corridor from Casper to Rock Springs. Gusty winds persist into
Saturday as a disturbance nears the state with portions of the
Bighorn Basin possibly seeing gusty winds as well.

There remains high uncertainty regarding the exact impacts from
the upcoming systems over the weekend. At this time models
still do not have a consensus in terms of two key components
which are the track and timing. Other factors like potential
upsloping and temperatures still need to be worked out and
could greatly change impacts seen across the state. A second
quick moving Canadian originating disturbance looks to move
south into the region as the first system begins to shift
towards the east on Sunday. This disturbance is forecast to
usher in even colder Canadian air for Sunday through Tuesday.
There is the potential for some locations east of the Divide to
see their first freeze of the season as a result of this colder
air. However, just how cold it may get depends on how far south
this disturbance goes which would lead to colder temperatures
and how much cloud cover there is. Overall, the weekend is
looking unsettled with multiple disturbances. These will bring
widespread chances for precipitation and high elevation
accumulating snow, along with the potential for some of the
coldest temperatures so far this fall.

&&

.DISCUSSION...
Issued at 103 AM MDT Wed Oct 1 2025

Southwest flow aloft will be in place over the Cowboy State today
through Friday, as a longwave trough develops off the West Coast and
gradually digs south over the Great Basin by Friday. There will be a
10% chance for showers over the western mountains today, as subtle
shortwaves move over the area through this flow. Some of these
showers could move into the central basins toward the later half of
the afternoon. Temperatures will be cooler east of the Divide, but
still slightly above normal in the lower to middle 70s. Dry and
warmer conditions will be in place Thursday, as 500mb heights build
from a 591dm high over NM as well as the trough beginning to dig
south over northern CA. This will lead to highs in the lower 80s
returning to areas east of the Divide and slightly above normal
temperatures elsewhere.

Increasing chances for showers and thunderstorms will occur over
western portions Friday afternoon, as the eastern fringes of the
storm system approach the Cowboy State. The associated cold front
will reach far northern portions of the Bighorn Basin and western
portions of the state, leading to highs in the upper 60s to near 70
degrees. Breezy conditions will occur east of this boundary, along
and east of a Rock Springs-to-Buffalo line. Elevated fire weather
conditions will occur within this area as a result of the increased
southwest winds, occurring over the Wind Corridor (Rock Springs to
Casper) Friday afternoon. Critical RH values are not expected at
this time, but there is a high likelihood of wind gusts up to 35 mph.

The cold front will progress eastward through the overnight hours
Friday night, with showers remaining possible over western portions
through the night. Snow levels will be around 9500 ft, dropping as
low as 8500 ft by 12Z Saturday. Widespread showers are expected
Saturday, as the storm system moves over the region and exits over
the Northern Plains by 12Z Sunday. Temperatures will be 15 to 20
degrees colder Saturday as a result. Windy conditions with gusts up
to 50 mph will be possible across portions of Sweetwater County and
northern portions of the Bighorn Basin, as the main trough axis
moves over eastern WY. Additionally, there is a 10% chance for gusts
up to 60 mph near Buffalo Saturday night. Snow levels could drop as
low as 7000 ft over western portions during the day Saturday, and
range between 6000 and 7000 ft across the CWA Saturday night.
Needless to say, temperatures will be much colder Saturday night
with readings in the middle to upper 20s in the western valleys.
Lows in the middle to upper 30s expected east of the Divide and
Sweetwater County.

A second system that has been progged dropping south from Canada on
Sunday is still in the forecast, however it looks to come more in
phase with the exiting storm and bring a much colder Canadian air
mass to the Cowboy State as it sweeps eastward. This could lead to a
chance for snow for far northern portions of the Bighorn Basin, like
Cody and Lovell. This would also result in snow levels dropping to
6000 ft over the Bighorns. At this point, Sunday will be a pretty
raw, fall day, with highs in the lower to middle 50s under mostly
cloudy skies. Precipitation chances will be widely scattered at this
point, as any moisture will be residual with no strong forcing
mechanisms in place. Models continue to trend toward developing a
positively-tilted trough/cutoff low over the Great Basin/northern CA
Monday. The Cowboy State could be caught in an area of weak steering
flow or a building ridge from the cutoff low. Either way,
indications continue to point toward quieter conditions early next
week.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1030 PM MDT Wed Oct 1 2025

VFR conditions expected for the entirety of the period at all
TAF sites. Mainly clear skies overnight with light winds less
than 6-8kts. Winds will increase after 19-20Z west of the Divide
with daytime heating and mixing to the surface. Upper level
clouds will increase through the afternoon and evening. A light
breeze at RIW/LND in the afternoon as well before diminishing
winds at all locations after 00-01Z towards sunset with
radiational cooling. Dry conditions with no other weather
elements expected at this time.

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...
None.

&&

$$

UPDATE...Dziewaltowski
DISCUSSION...LaVoie
AVIATION...Lowe