281
FXUS65 KRIW 040301
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
801 PM MST Sat Jan 3 2026

.KEY MESSAGES...

- Winds increase this evening over portions of central WY with
  periodic gusts of 45 to 55 mph at times. Stronger gusts of 60
  mph or more cannot be ruled out at times.

- Precipitation begins to spread across western WY late this
  evening with periods of moderate to heavy snowfall possible at
  times through the day Sunday.

&&

.UPDATE...
Issued at 1157 AM MST Sat Jan 3 2026

Not much to update regarding the previous discussion as little
has changed in terms of the short term forecast. Mild and mainly
quiet conditions are expected across the state for much of the
day today. Precipitation moves into western WY late tonight into
the early morning hours on Sunday. Around the same time winds
will begin to increase over portions of central WY. As for snow
accumulations, amounts have seen little to no changes with
maybe a few locations seeing slight adjustments but nothing
noteworthy. Winter Weather Advisories remain in place across the
mountains of western WY and will go into effect shortly before
midnight tonight. Snow will continue periodically over western
WY through Sunday into Monday. Locations east of the Divide look
to remain mild and mostly dry through this time. The heaviest
precipitation comes to an end late Monday morning with some
light showers linger over western WY. The longer range forecast
has seen little change with the previous discussion doing a good
job of explaining what to expect for the upcoming week.

&&

.DISCUSSION...
Issued at 131 AM MST Sat Jan 3 2026

A transitory ridge will move over the region today, as a strong
closed upper low moves over the EPAC toward the West Coast. Dry
conditions and above normal temperatures will be in place across
much of the CWA once again as a result (especially east of the
Divide). Gusty winds will develop over the Wind Corridor (eastern
Sweetwater County to southern Johnson County) this afternoon,
with southwest gusts of 25 to 35 mph developing by 17Z. Similar
wind gusts will develop off the east slopes of the Absaroka,
Bighorn and Wind River Mountains, with locally higher gusts of
50 to 60 mph occurring over South Pass/Red Canyon.

A leeside trough will develop over eastern WY after 00Z Sunday, due
to southwest winds aloft as the ridge transitions eastward. Winds
will be increasing over the aforementioned areas during this time,
with gusts of 35 to 50 mph. The western mountains will be included
in these areas as well. High winds (gusts 60+ mph) will be likely
over South Pass/Red Canyon, as those 50 to 60 mph gusts continue
through the overnight hours, decreasing after 09Z. There is
still a chance for high winds, with a 30 to 50% chance, for
these to also occur over Hwy 258 on the south side of Casper
between 06Z and 15Z Sunday.

The timing for the next round of snow for western portions has
shifted once again toward this evening, as the first shortwave from
the upper low looks to reach western portions by 06Z. Initial
snowfall will be confined to the far western mountains this evening,
with snow increasing across the rest of the west by 06Z as the
shortwave passes overhead. This will be a short burst of snow in the
mountains, with rates up to 1"/hr. Precipitation is expected to stay
as snow in the western valleys, as 700mb temperatures will be around
minus 4C (which correlates to a snow level of 6500ft. This will not
be an exact repeat from last Thursday, as the strong inversion will
not be in place today ahead of the precipitation. Accumulations of 1
to 2 inches is possible in the Jackson/Star Valleys tonight.
Precipitation will become more scattered across the west after 12Z
Sunday, becoming more widespread by mid to late afternoon as the
second shortwave arrives. The PFJ will arrive as well, with the left
front quadrant of the jet being over northwestern portions. This
will be conducive for better lift and lead to higher snowfall
totals. Snow will begin to wane by Monday afternoon, as the jet
shifts southward. Snowfall amounts of 8 to 16 inches is expected
through Monday morning, with locally higher amounts of 18 to 24
inches in the Tetons/Gros Ventres and southwestern Yellowstone (the
Pitchstone Plateau). Will issue Winter Weather Advisories as a
result.

For the rest of the CWA, temperatures will continue to be above
normal, with highs in the middle 40s to middle 50s Sunday, dropping
a few degrees on Monday. There is a 20 to 30% chance for showers
during the day Sunday over Sweetwater and southern Lincoln counties,
crossing the Divide into central portions. Little to no rain is
expected with these showers for now. Winds will remain gusty, but
high winds are not expected during the day Sunday. A longwave trough
will develop off the West Coast by 00Z Monday, with the base of the
trough digging southward just off the coast of central CA. The
trough will slowly make its way onshore and develop a closed low at
the base of the trough through 00Z Tuesday. This will lead to the
moist southwest flow pattern, and the PFJ, to shift southward (as
previously mentioned). The northern end of the trough will separate
from the closed low and bring a more west-northwest flow pattern to
the region Monday night into Tuesday. This also looks to be a
precursor to colder temperatures by mid-week or late in the week
next week.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 330 PM MST Sat Jan 3 2026

VFR conditions at all locations to start the period with gusty
winds at CPR up to 25-30kts and increasing high clouds into the
overnight hours. Snow chances increase at JAC after 07Z and
spreads to BPI/PNA after 10-11Z. MVFR conditions expected after
this point with possible IFR conditions by sunrise Sunday
morning after 12Z through most of the period into the
afternoon/evening hours. East of the Divide will see increasing
winds ahead of this system at COD/CPR up to 30-35kts
respectively that will remain elevated through the entirety of
Sunday after 12Z. RIW/LND will push up to 18kts after 18Z
through sunset with mid to upper level ceilings remaining
throughout. Dry conditions expected to remain east of the
Divide.

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...
Winter Weather Advisory from 11 PM this evening to 11 AM MST
Monday for WYZ001-012-014-024.

&&

$$

UPDATE...Dziewaltowski
DISCUSSION...LaVoie
AVIATION...Lowe