Grand Targhee

000
FXUS65 KRIW 211726
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1126 AM MDT Wed Oct 21 2026

.KEY MESSAGES...

- Above average temperatures continue today and Thursday ahead 
  of the next storm system. 

- Increasing rain chances Thursday morning and throughout the
  day with mountain snow likely for western mountains later in
  the afternoon and overnight into Friday, spreading to eastern
  mountains Friday evening. 

- Wind ramps up starting Thursday, strongest Friday east of the
  Divide and across the wind corridor with gusts ranging from 40
  to 55 mph (80-90% confidence). This will also lead to elevated
  fire weather concerns east of the Divide.

- A cold front pushes through Friday morning, bringing cooler
  temperatures to near seasonable heading into the weekend as
  well, reinforcing snow chances lowering to 8-9kft to impact
  mountain passes for Friday evening and Saturday morning.

&&

.DISCUSSION...
Issued at 130 AM MDT Wed Oct 21 2026

IR currently depicts mid level clouds pushing in across western
and northern parts of the CWA from the southwest, extending from
Baja Californian moisture extending through the Four Corner
Region. WV imagery shows the main finger of the PFJ extending
across southern Canada and a strong upper level low off the
central Californian coastline. This low will begin its eastern
extent Wednesday night into Thursday as it becomes a more open
and progressive wave that will strengthen the southwest and
divergent flow into the CWA out of northern Utah. This is where
the stronger PVA anomalies will occur extending moisture content
into southern portions of the state by Thursday morning. 

The aforementioned PFJ will start to dip across the Pacific
northwest aligned with the main low as it becomes more open late
Thursday with an increasing jet max pushing 120-130kts. This
deepens the northern portions of this system with increased
divergence aloft. This increases the pressure gradient across
much of the CWA about 5 to 7 mb across the state, strongest
across the south. Southwest winds push 40 to 55 mph Thursday
afternoon during peak heating and mixing to the surface,
strongest across the wind corridor from Sweetwater through
eastern Fremont to Natrona Counties. Occasional gusts over 60 to
65 mph possible (40-50%) for the higher terrain areas of South
Pass and outer drive of Casper Mountain. There is low confidence
on high wind criteria being met for this period of time, but
winds remain elevated overnight into Friday morning with wind 
shifts occur due to a passing cold front extending through the 
CWA into the afternoon hours Friday. 

Precipitation wise, expect shower activity to increase out of
northern Utah into southern portions of the CWA Thursday 
morning pushing north throughout the day. Much of the QPF will 
fall west of the Divide with some higher terrain mountain snow 
expected by late Thursday afternoon and especially overnight as 
temperatures fall. This will be reinforced with FROPA on Friday,
lowering freezing levels to 8-9kft as the system shifts east of
the Divide, and thus, impacting the Bighorns with mountain 
snow. Mountain passes, to include Teton, Togwotee, and South
Pass, extending to Granite/Powder River, will see the impacts 
and hazards late Friday and into Saturday morning as the trough 
shifts northeast by day's end Saturday. Probabilities for 
snowfall totals look to be of higher confidence across western 
mountains, to include the Winds, of 6 inches or more around 
60-70%. The Bighorns are of lower confidence around 30-40% for 
later Friday and into the overnight hours. With snowfall totals 
of not great confidence, and being Friday for impacts, it has 
been decided to include surrounding offices to not issue any 
headlines at this time. Model guidance has been up and down the 
past couple of days with this round bumping totals up once again
and will need higher confidence to do so moving forward. 

Beyond that, expect more seasonable to just below average
temperatures post FROPA Friday and into the weekend to fell more
Fall-like for this time of year moving towards the later half of
October. Another low extending out of the Gulf of Alaska looks
to push down along the L/W pattern into the Pacific northwest
late Sunday that will near the CWA early next week. This will
not only reinforce this cooler air but continue the active
pattern that has a better track for stronger snow totals. Too
soon to judge the impacts at this point in time, but this looks
to have a better track for higher mountain snow along and west
of the Divide. Stay tuned for forecast updates and any headline
issuance later Wednesday or Wednesday night as confidence grows
for impacts on Friday into Saturday.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1125 AM MDT Wed Oct 21 2026

VFR flight conditions are largely forecast through 18Z Thursday. 
There is a 10% to 20% chance of a rain shower at or around 
KJAC, KRKS, and KCPR between 23Z Wednesday and 08Z Thursday, at 
the latest. Given the low confidence in occurrence and impacts,
there is no mention in TAF at this time. There is also a 10% to
25% chance of MVFR clouds or fog at KJAC, KCPR, KRIW, KPNA, 
KBPI, and KLND early Thursday. The higher chances exist at KCPR,
KJAC, KPNA, and KBPI so added a FEW or SCT cloud group at 025 
or 035 at this time. Breezy winds are forecast at KRKS and KCOD 
this afternoon, KRIW and KLND after sunset, and at KCPR after 
sunset Thursday morning. Winds remain relatively light at all 
other terminals.

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.

&&

$$

DISCUSSION...Lowe
AVIATION...Gerhardt