722
FXUS65 KRIW 121917
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
117 PM MDT Sun Oct 12 2025

.KEY MESSAGES...

- Gusty 35 to 45 mph west winds across the Wind Corridor
  decrease to 20 to 30 mph early this afternoon and subside by
  sunset tonight.

- Isolated to widely scattered (15-40%) light showers and
  mountain snow continues across western and northwestern
  Wyoming through the evening.

- Widespread freezing temperatures tonight with temperatures in
  the 20s and low 30s. A Freeze Warning is now in effect late
  tonight/Monday morning across the eastern Bighorn Basin and
  northern Johnson County.

- Precipitation chances (up to 40%) return Monday afternoon
  across southern Wyoming. Gusty winds, showers, thunderstorms,
  and mountain snow will accompany the next weather system
  Tuesday through Thursday.

&&

.UPDATE...
Issued at 116 PM MDT Sun Oct 12 2025

The forecast remains mostly unchanged this afternoon with the upper-
level trough that brought yesterday`s unsettled weather now (19Z)
located over eastern Montana. It`s associated upper-level jet
maximum is roughly located over the Wind Corridor and is
contributing to gusty 35 to 50 mph winds across that area. As the
entire system progresses east this afternoon, these gusty winds will
subside slightly. Cold air advection behind the trough will favor
gusty west winds of 20 to 30 mph through sunset this evening.

Lingering moisture from the departing system is present across
western and northwestern Wyoming, evident on satellite by cloud
cover. This moisture will remain over these areas until the evening,
and with much colder air and westerly flow, isolated to widely
scattered (15%-40% chance) terrain induced showers and mountain snow
remains possible through sunset. However, light precipitation could
linger across Yellowstone National Park until midnight.

As mentioned, cold air has filtered into Wyoming behind the system
with temperatures 10 to 20 degrees cooler at 19Z compared to 19Z
yesterday. Widespread below freezing temperatures are still forecast
tonight with the cold air already in place and clear overnight
skies. As for the Freeze Watch area (the eastern Bighorn Basin and
northern Johnson County), confidence in how widespread a hard freeze
(28 degrees or lower) will be is around 40%. However, given the
clear skies and already cold conditions, we went ahead and upgraded
the Freeze Watch to a Freeze Warning. Otherwise, the forecast for
Monday remains on track with isolated showers across southern
Wyoming as southwesterly flow returns to the Intermountain West with
weak embedded disturbances aloft.

&&

.DISCUSSION...
Issued at 127 AM MDT Sun Oct 12 2025

Thunderstorms are exiting northward into the BYZ CWA as of 06Z. The
cold front has passed through Greybull and Riverton and will
progress eastward, exiting the CWA by sunrise this morning. Wind
gusts of 35 to 45 mph will continue across much of the area this
morning, decreasing after 18Z (12 PM). Light precipitation will also
continue over northern portions through the morning, with light snow
in the higher elevations as well as the Wind River Mountains and
Salt and Wyoming Ranges. Isolated showers will then be possible over
western portions through the afternoon. A Freeze Watch remains in
effect for eastern portions of the Bighorn Basin and northern
Johnson County, as temperatures have trended upward closer to 30
degrees and making the chances for a hard freeze less likely. Have
continued with the Watch for now, as skies will become clear early
this evening. Temperatures across the CWA have trended upward as
well, with readings near 30 degrees for most locations east of the
Divide. Readings in the teens are no longer in the forecast for the
western valleys, although locations in the Upper Green River Basin
could still be that cold.

Breezy southerly winds return Monday, with isolated showers possible
over the southern half of the forecast area. Temperatures will be
about 10 degrees warmer west of the Divide, as a result of the
southerly winds. This trend continues Tuesday, as a strong closed
upper low from British Columbia digs southward just off the West
Coast. Southerly winds will be a bit stronger with this digging
trough, especially across the Wind Corridor (Rock Springs to
Casper). Rain showers will be confined to far western portions
of the CWA.

Models have come into better alignment and bring this storm closer
to the Cowboy State during the day Wednesday. Rain showers will be
ongoing over far western portions Wednesday morning, with snow
levels ranging between 7500 and 8500 ft over the Tetons due to the
proximity of the associated cold front. These showers will become
more widespread through the day. Southerly winds will continue to
increase, with gusts of 35 to 45 mph likely across much of the area.
Coincidentally, this system is progged to play out quite similarly
as the current ongoing storm. The cold front will make its way
eastward over western portions through the day, quickly making its
way across the rest of the CWA through much of the night. There is a
chance for high winds (60+ mph gusts) to occur over portions of
Natrona County in the wake of the front. This system is not expected
to be as cold either, with snow levels ranging between 6500 and 7500
ft Wednesday night as the closed upper low moves over eastern MT by
12Z Thursday. Precipitation chances will continue Thursday, mainly
over northern portions, as winds turn more northwesterly. Gusts up
to 35 mph will be likely over northern portions of the Bighorn Basin
and Johnson County, as well as the Green River Basin and Sweetwater
County.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1030 AM MDT Sun Oct 12 2025

VFR conditions expected throughout the period for all TAF sites.
Breezy winds at most locations, with CPR being strongest to
start with gusts up to 35-40kts. Winds will diminish through the
afternoon and skies improve scattering out to the mid and upper
levels as the upper level low and associated cold front push
further east. Expect light winds less than 10kts and mainly
clear skies towards sunset after 01Z through the overnight due
to radiational cooling. This will remain so through the end of
the period for Monday morning as well. No other weather
elements are 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...
Freeze Warning from 3 AM to 9 AM MDT Monday for WYZ004-006-010.

&&

$$

UPDATE...Gerhardt
DISCUSSION...LaVoie
AVIATION...Lowe