391
FXUS65 KRIW 091117
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
417 AM MST Tue Dec 9 2025

.KEY MESSAGES...

- Moderate snowfall will continue across the NW higher
  elevations today and through Thursday. Total snow accumulation
  through Thursday will reach 2 to 3 feet. Warmer valley
  temperatures will inhibit most snowfall accumulations.

- Very windy across much of the state today, with High Wind
  Warnings in effect for much of southern and central Wyoming.

- Temperatures remain 10 to 20 degrees above normal

&&

.DISCUSSION...
Issued at 145 AM MST Tue Dec 9 2025

The next passing shortwave energy is beginning to impact the NW
higher elevations this morning, and the overall flow the next
several days continues to be favorable for continued snow
accumulation. Between orographic lifting and the passing wave,
accumulations of 2 to 3 feet are becoming more likely for the
Tetons and Absarokas, with 6 to 12 inches for remaining higher
mountain ranges and the greater YNP region. Current variety of
winter warnings and advisories are well positioned, so no
adjustments needed at this time. In a usual winter, temperatures
would be cold enough to help get some of this precip into the
lower valleys, but not this year. Temperatures today will be in
the 40s for the western valleys, and in the low 50s for the
lower elevations east of the Divide, so snowfall will be locked
into the mountains for the remainder of the week.

The core of the llvl jet streak will be passing by just to the
north today, and with temperatures in the 50s, a large chunk of
this wind energy will mix to the sfc during the afternoon. With
H7 winds at 70kts as they pass by, peak sfc wind gusts of 50 to
60 mph are likely for southern WY stretching NE into the Casper
vicinity. The only question is winds across northern Johnson
County late this afternoon as the cold front barrels through.
While winds sfc and aloft are aligned, models are not really
bringing winds up until the system gets a little farther east.
Will monitor this if High Wind Warnings are needed there.

Beyond this, the H5 ridge along the Rockies doesn`t move much
through the weekend, deflecting weather systems to the north and
east, and keeping the unusually warm temperatures in place.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 410 AM MST Tue Dec 9 2025

The most impacted terminal over the next 24 hours will be in
vicinity of KJAC where an approaching weather system will bring
periods of rain and snow through much of the period. Conditions
will be generally MVFR, although brief periods of IFR are
possible in heavier periods of precipitation. We also added
light snow to KPNA after 04Z Wednesday as the system drops
southward. Otherwise, largely VFR conditions are expected. Minimal
chances at COD/WRL/CPR after 19Z carrying only VCSH through
01Z. Otherwise, windy conditions throughout the period remaining
elevated overnight. Strongest winds at COD/JAC/RIW up to 30
knots with RKS and KCPR up to 45kts with a 30 percent chance of
gusts over 50 knots, especially between 17Z and 01Z. Wind will
remain elevated overnight but not as strong as during the day.
Other locations will be breezy but less winds up to 18-25kts.
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 Storm Warning until 5 PM MST Wednesday for WYZ001-002.

Winter Weather Advisory until 5 PM MST Wednesday for WYZ008-
014-015-024.

Winter Storm Warning until 5 PM MST Wednesday for WYZ012.

High Wind Warning until 2 PM MST this afternoon for WYZ016.

High Wind Warning until 5 AM MST Thursday for WYZ019-020-022-
027>030.

&&

$$

DISCUSSION...Straub
AVIATION...Hattings