615
FXUS65 KRIW 120139
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
739 PM MDT Fri Sep 11 2026

.KEY MESSAGES...

- A weak cold front will bring cooler temperatures into
  northern Wyoming tonight, bringing overnight low temperatures
  closer to normal in the 40s.

- More seasonable temperatures over the weekend with breezy
  winds across southern Wyoming. Skies will remain mostly clear,
  mostly clear skies expected.

- A stronger and mainly dry cold front pushes through late
  Sunday that will bring cooler air to start the new work week
  Monday. Temperatures will fall to near freezing west of the
  Divide, and low 40s to the east.

&&

.UPDATE...
Issued at 1245 PM MDT Fri Sep 11 2026

IR and radar continues to show clearing west to east across the
CWA with the main finger of the PFJ well to the north on WV near
the Canadian border. An approaching cold front over southern
Montana will aid in not as warm temperatures this afternoon.
FROPA by late afternoon for northern parts of the area to near
sunset for the Wind River Basin to Natrona County before pushing
south before midnight. Breezy westerly winds ahead of FROPA with
northern flow behind it, being quite gusty up to 40 mph for
areas of the northern Bighorn Basin to Johnson County. Some
light showers possible (15-20%) for the northern Bighorns, but
nothing of consequence. A seasonable weekend in terms of
temperatures ahead of the next system and front Sunday. This
will be mainly dry but with a more potent cold push dropping 10
to 15 degrees for morning lows and afternoon highs on Monday.
Beyond that, not much to speak of with a relatively benign
forecast going forward.

&&

.DISCUSSION...
Issued at 158 AM MDT Fri Sep 11 2026

Moisture has finally arrived over the Cowboy State, ending this
prolonged streak of critical fire weather conditions. Partly to
mostly cloudy skies continue over the state this morning,
scattering out by midday day. Isolated showers to the west of
PIH and SLC will continue to track eastward this morning and
move over far western portions of the forecast area around 10Z.
Virga is likely from these showers, but amounts around 0.05"
will be possible over the Tetons/Gros Ventres and toward
Union/Togwotee Pass. These showers may cross the Divide and move
over the Upper Green River Basin, after sunrise this morning,
but will likely stay as virga. These showers are expected to end
by 18Z, with dry conditions expected through the rest of the
day. There is a 10% chance for virga showers over areas east of
the Divide late in the afternoon as a cold front drops
southward.

Widespread gusty winds will be the main concern again today,
with west wind gusts of 25 to 35 mph occurring across the CWA
this afternoon. The exception will be portions of the Bighorn
Basin and the northern half of Johnson County. Northwest wind
gusts up to 30 mph will occur in these areas as a cold front
progresses southward through the afternoon. The front will pass
through the Bighorn Basin and Johnson County by 00Z Saturday
(6pm), quickly reaching the Casper area and Riverton between 01Z
and 03Z, eventually becoming stationary along the Divide by
06Z. Temperatures will much cooler today, especially east of the
Divide, running about 5 to 10 degrees cooler. This will apply
to far northern portions, due to the proximity of the front.

Models have become aligned with the much talked about storm
system for this weekend, with not much change from yesterday
with the forecast track. The storm system is still forecasted to
drop southward along the West Coast tonight into Saturday. The
aforementioned cold front will gradually retreat northward
Saturday afternoon, due to an increase in southwesterly winds.
The front looks to get pushed into the Bighorn Basin and further
north into Sheridan County through Saturday afternoon. Apart
from isolated showers and thunderstorms over eastern portions of
Sweetwater County Saturday afternoon, conditions are expected
to remain dry. Precipitation chances continue to be pushed
northward as the storm stays further north in MT. Little to no
precipitation is now expected from this storm. The associated
cold front will push through the Cowboy State Sunday night,
clearing the forecast area by 12Z Monday. Sub-freezing
temperatures will return to western portions Sunday night/Monday
morning, with readings in the upper 30s to lower 40s elsewhere.
Dry and cooler conditions will be in place Monday, with highs
in the 60s to near 70 degrees across the area. Conditions will
remain dry with seasonal temperatures Tuesday. A storm system
may impact the region Wednesday, but confidence is low at this
point as colder, Canadian airmasses begin to drop southward.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 351 PM MDT Fri Sep 11 2026

VFR conditions prevail through the period. Winds remain gusty for
some east of the Divide locations this evening in the wake of a cold
front. However, winds should eventually decrease overnight. Post-
frontal MVFR to IFR clouds are possible around KCOD, KCPR, and KLND
through Saturday morning. Winds begin to increase late Saturday
morning to early afternoon for locations west of the Divide, with
gusts generally 15 to 25 knots.

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...Lowe
DISCUSSION...LaVoie
AVIATION...Wittmann