491
FXUS65 KRIW 260000
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
600 PM MDT Fri Sep 25 2026

.KEY MESSAGES...

- Isolated showers push east out of the area this evening, with
  dry conditions tonight.

- It will remain warm for most of the area through the weekend.
  A bit cooler for western valleys.

- Breezy west to southwest winds each afternoon through Sunday,
  especially across the Wind Corridor and higher elevations.
  Tonight, gusty winds are expected for northern Yellowstone,
  the Absarokas, and eastern slopes of the Wind River Mountains.

- Showers and thunderstorms are forecast Sunday afternoon
  through Tuesday morning across western and central Wyoming.
  Elevations above 10,000 feet could see a few inches of snow.

&&

.UPDATE...
Issued at 1201 PM MDT Fri Sep 25 2026

Midday satellite water vapor imagery shows a shortwave traversing
Wyoming, with accompanying mid-level moisture. This shortwave and
mid-level moisture will support isolated showers and thunderstorms
across northeast Sweetwater, southeast Fremont, Natrona, and Johnson
Counties through the afternoon. Should a thunderstorm occur, eastern
Natrona and far southern Johnson Counties would be most likely
locations. This is due to forecasted BLCAPE values around 250 J/kg
to 500 J/kg along a weak frontal boundary. It is important to note
that most areas will remain dry today with plenty of sun,
afternoon southwest wind gusts, and highs in the 70s.

As mentioned in the morning discussion, a cold front will slowly
shift into northwest Wyoming late tonight. This cold front will keep
winds gusty well into the overnight hours across northern
Yellowstone, the Absarokas, and eastern slopes of the Wind River
Mountains. West to southwest wind gusts of 30 to 40 mph, and up to
50 mph for the highest elevations, are forecast for the
aforementioned locations. The remainder of the forecast remains on
track with showers and thunderstorms Sunday afternoon through
Tuesday morning.

&&

.DISCUSSION...
Issued at 100 AM MDT Fri Sep 25 2026

IR currently depicts mainly clear skies for the northern half of
the CWA with mid and upper level clouds spilling in from the
south for southern portions of the state from a weak trough
across northern Colorado. WV shows the main finger of the PFJ to
the north dipping down from the Gulf of Alaska to the Pacific
Northwest around the next main L/W trough that will affect the
upper Rockies by Sunday. For Friday, expect a bit warmer than
average temperatures and gusty winds due to an increasing
pressure gradient ahead of an approaching west to east moving
cold front Friday night into Saturday morning. Gusty winds 15 to
25 mph will be common for much of the area in the afternoon
during peak heating and mixing, stronger for the Wind Corridor
from Sweetwater to Natrona Counties where gusts could reach 30
to 35 mph. Winds look to weaken but remain elevated after sunset
as the aforementioned cold front starts to push in out west
before stalling along the Divide by sunrise Saturday morning. A
little bit of model disagreement on how far it reaches, but
overall, dry conditions will be expected. With the weak trough
to the south, expect some isolated rain showers and
thunderstorms to push across far eastern reaches of Sweetwater
County through Muddy Gap to Casper early to late afternoon with
minimal accumulations and/or impacts expected. Otherwise,
increased clouds throughout the CWA in the mid and upper levels
ahead of the deepening trough to the west with increased
divergence aloft ahead of it.

More seasonable temperatures west of the Divide Saturday with a
bit above average to the east, dependent on how far east the
cold front pushes. Gusty winds continue Saturday as well similar
to Friday. As the main low skirts to the north across southern
Canada late Saturday into Sunday, the southern end of the trough
begins to cut off near California. This will deepen as well with
the increased upper level divergence as it progresses slowly
eastward bringing the more conducive southwest flow across the
CWA. Expect scattered shower activity west of the Divide late
Sunday morning, expanding to the east later Sunday evening and
into the overnight hours and into Monday morning. The low pushes
east, across the Southern Rockies and into the High Plains by
Tuesday that will end precipitation chances. Accumulations at
this time don`t look overwhelming, but all areas have a decent
chance for a wetting rain (>.1") around 50 to 90% in coverage,
and again best chances west of the Divide. Mountain snow is
likely as well, as temperatures become more seasonable and
freezing levels drop to the 10-11kft range. An inch or two is
possible in the higher elevations of the Winds (mainly the
western side), along with the Absarokas and northern Bighorns.
Any mountain passes should stay void of any snowfall but there
is time for change being a few days out. Stay tuned for updated
forecasts in the coming day or two for the models to come into
better agreement on the movement of the cut-off low from
California through the southern Rockies.

Beyond Tuesday, expect upper level ridging to build back in from
the southwest for the rest of the week and into the weekend.
Temperatures will moderate back to seasonable Wednesday onward
with dry conditions expected there on. The next system looks to
impact the CWA and Northern Rockies heading into the following
weekend looking at the longer term model solutions but time will
tell.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 345 PM MDT Fri Sep 25 2026

VFR conditions expected across the area through the TAF period.
Mid to high level clouds, SCT-OVC FL120-250, will be over
Johnson/Natrona counties by the start of the period and continue
to exit eastward. Additional FEW-SCT clouds will push in from
the west after sunset this evening.

Wind gusts around 20kt will begin to decrease for several
terminals, with light winds through 18Z. Wind gusts of 20 to
25kt will be widespread west of the Divide after 18Z. These
winds will begin to spread into the central basins and the
Casper area between 20Z and 22Z Saturday. A cold front will
move southward through Johnson/Natrona counties after 09Z,
turning winds northerly. This front will also reach KCOD by 11Z,
which could bring lower clouds to the terminal. However, there
is currently a less than 10% chance for MVFR ceilings or lower
to occur.

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