904
FXUS65 KRIW 021913
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1213 PM MST Tue Dec 2 2025

.KEY MESSAGES...

- Light snow showers will continue across portions of western WY
  today, with showers making their way east of the Divide later
  this evening.

- Snow showers will be possible east of the Divide Wednesday
  morning with snow amounts ranging from a coating to an inch
  or two.

- Confidence continues to grow for a long duration event over
  western WY for the end of the week into the weekend. Early
  indications show the potential for the first noteworthy
  snowfall of the season for western mountains.

&&

.UPDATE...
Issued at 1208 PM MST Tue Dec 2 2025

Not much of a change in regards to the short term forecast.
Temperatures are expected to be warmer than the past few days with
highs in the mid to upper 30s and possibly near 40 east of the
Divide. Western WY due to cloud cover and precipitation will be
slightly cooler with highs in the low 30s. Winds will be breezy
to gusty at times across parts of the state this afternoon
before gradually weakening after sunset. Overall, the forecast
remains on track with light snow continuing to fall across
portions of western WY this afternoon and evening. Locations
east of the Divide can expect to see snow showers develop late
this evening and spread south through the morning hours on
Wednesday. As mentioned in the previous discussion, snowfall
amounts east of the Divide will be mainly confined to
orographically favored locations. This would include eastern
slopes of the Wind River Range such as the Lander Foothills,
parts of Casper Mtn, as well as some portions of the Bighorn
Basin. Hi-res models to support this as many show snow
accumulations of 1 to 2 inches (60-70%) with isolated pockets of
3 inches (20-30%) possible by late Wednesday morning. Other
locations east of the Divide look to see lesser amounts ranging
from a trace to maybe an inch. The main factor is the lack of
orographic support to keep snow over the area. Instead showers
will likely move across central basin locations for brief
periods before moving out of the area leading to lesser amounts.
The higher elevations can expect to see an additional few
inches of accumulating snow through Wednesday morning. The most
favored locations will be across the Tetons, Wyoming and Salt
River, eastern Wind River, and northern Bighorn Ranges.

As for the longer range forecast going into the end of the
week and weekend. Models continue to indicate a higher
possibility for the first real noteworthy snowfall over western
mountains. Early indications show amounts of a foot or more by
the end of the weekend over western mountains with lower
elevations valleys possibly seeing multiple inches as well. This
looks like it may be a longer duration event with a brief break
at times but mainly consistent snowfall is likely over the
western mountains for multiple days. This event is still
multiple days out so some variation is possible but as of today
confidence is growing so it will be worth monitoring over the
next few days.

&&

.DISCUSSION...
Issued at 1254 AM MST Tue Dec 2 2025

The first round of snow has already passed over northwestern
portions, between 03Z and 06Z. There will be a lull for a few hours
before snow returns by 12Z this morning, as the main storm system
approaches from MT. Snow flurries will be possible through the rest
of the night east of the Divide. As snow redevelops over far
northwestern portions and the Bighorns, snow chances will increase
across western portions of the CWA through the morning hours and
continue through the day and evening. Snow will develop east of the
Divide after 00Z, as the cold front enters the area and progresses
southward. This area will be the focus for the snowfall tonight, as
snow ends across the west by 06Z (11pm). Forecasted snowfall amounts
have trended downward, with most locations east of the Divide being
an inch or less. A few orographically-favored locations look to get
2 to 3 inches, like the south side of Casper, Lander and Meeteetse.
2 to 3 inches is also forecasted in the Star Valley, due to
favorable dynamics. Locally higher amounts of 4 to 5 inches on the
east side of the valley cannot be ruled out. Otherwise, snowfall
amounts in the mountains will be highly variable ranging between 1
to 4 inches. The Tetons, Salt/Wyoming Ranges and the far north end
of the Bighorns will have the highest amounts of 4 to 6 inches. West
to northwest winds, with gusts of 35 to 45 mph, will continue over
the east slopes of the Absaroka and Wind River Mountains as well as
southern portions of Fremont and Natrona counties this morning and
through much of the day today. These conditions will occur at
Dubois, Cody and Clark as well. Gusts of 50 to 55 mph will also
occur along Hwy 258 on the south side of Casper. Gusts of 25 to 30
mph will then be common after 18Z across areas west of the Divide
and portions of the Wind River Basin. Northerly winds gusting 30 to
40 mph will occur over Johnson County and northern portions of the
Bighorn Basin after 22Z, as the cold front begins its southward
progression. Reductions in visibility due to blowing snow will be
brief, as the snowfall will be light tonight.

Snow will be ending across the area during the predawn hours
Wednesday morning, with a few locations of lingering snow through
the rest of the morning. Conditions will remain dry Wednesday night
and Thursday, temperatures moderating a few degrees on Thursday.
Details for the end of the week and into the weekend continue to
change. Models have trended toward a fast moving cold front moving
over the area Thursday night and exiting the area through Friday
morning. This system would bring another chance for widespread snow
east of the Divide and western portions. Chances for accumulating
snow over the western mountains continue to look good from Friday
afternoon into Saturday.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1101 AM MST Tue Dec 2 2025

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals

To start the period, models have backed off on and moved
precipitation for the afternoon across the Jackson Valley farther
south (towards Star Valley) so cigs and vsby with snow showers has
been adjusted in the TAF to reflect prevailing VFR conditions. That
being said, there may still be a period of light snow showers and
MVFR conditions during the first few hours of the period at KJAC,
which is noted with a TEMPO group.

At other terminals, snow shower chances will be lesser (30 to 40%)
and generally will be more isolated in nature, particularly at KBPI
and KPNA this afternoon and again overnight. Overnight, a cold front
will move through, but will generally be much weaker once it crosses
the Divide, so snow shower chances are less likely with the front.
At KRKS however, once flow becomes northeasterly behind the front,
expect gusts to increase and snow showers to remain possible along
with MVFR to even occasional IFR conditions. MFVR or near MVFR
conditions and gusty northeast winds will likely linger through the
end of the period at KRKS.

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals

The main forecast concern today will be a cold front, which will
slide southward beginning around 00Z, impacting most east of the
Divide terminals overnight. With the cold front, expect snow
showers, IFR cigs, and gusty north winds. Timing has changed
slightly since the previous forecast, with the main impacts from the
front being later than the previous forecast by 1 to 2 hours. IFR
conditions will linger longest at KLND and KCPR into Wednesday
morning. Most other terminals will see improving conditions and even
improvements to VFR after 12Z.

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...
Winter Weather Advisory until 11 PM MST this evening for
WYZ012.

&&

$$

UPDATE...Dziewaltowski
DISCUSSION...LaVoie
AVIATION...Hensley