820
FXUS65 KRIW 092003
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
103 PM MST Tue Dec 9 2025

.KEY MESSAGES...

- Moderate snowfall will continue across the northwest and
  northern WY higher elevations today and through Wednesday
  night, with periods of lighter precipitation and periods of
  heavier snowfall. Total snow accumulation through Thursday
  will reach 2 to 3 feet in some locations in the northwest
  mountains. Warmer valley temperatures will inhibit most
  snowfall accumulations. Winter Storm Warnings and Advisories
  continue through late Wednesday afternoon.

- Strong and gusty winds continue across much of the state
  today, with High Wind Warnings in effect for much of southern
  and central Wyoming. Wind gusts over 50 mph are also occurring
  in the higher elevations of the western and northwest WY
  mountains.

- Temperatures remain 10 to 20 degrees above normal through
  Thursday in the foothills and lower elevations, with some
  cooler air moving into northern WY Friday and Saturday.

&&

.UPDATE...
Issued at 102 PM MST Tue Dec 9 2025

The very energetic west-northwest moist flow pattern continues
over Wyoming this afternoon into Wednesday. A weak shortwave
trough in the flow is currently moving from central Montana into
northern WY enhancing snow/rain more over northwest and northern
WY this afternoon as higher surface pressure follows the trough
southward. Gusty north-northwest winds are expected across
northern WY through about 8 PM. With precipitation continuing
over the higher terrain, snow/rain should also push into the
northeast Bighorn Basin and Johnson County from about 3-6 PM.
Have opted to not issue a winter weather advisory or high wind
warning for northern Johnson County given the short duration of
the snowfall and winds in the 20-30 mph range with gusts 35-40
mph. This trough will push the mid-level moist WNW flow
southward back to mid-western WY overnight to bring light to
moderate snow back to the western WY mountains while it
decreases over the northern WY mountains. Another embedded
shortwave trough in this pattern then approaches after midnight
tonight, increasing precipitation over northwest WY, which will
continue over the winter storm warning area through mid- to
late-afternoon Wednesday. This trough will also increase mid-
level flow to 40-50 knots, which will increase winds over the
area again on Wednesday (after somewhat of a lull overnight).
Conditions appear to be increasing for strong downslope winds
along the Absarokas and Wind Rivers Thursday morning as well in
advance of some colder air pushing into northern WY Friday and
Saturday.

Have increased the winds in the forecast over the higher terrain
of the western mountains per feedback from higher elevation
observation sites and the avalanche center. QPF and snow
forecast are still consistent with previous forecasts.

&&

.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 low-level 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 /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1034 AM MST Tue Dec 9 2025

VFR conditions across nearly all terminals through the period with
the one exception being KJAC where a weather system will bring
periods of rain/snow. Rain/snow showers will periodically move
through KJAC for the start of the period. MVFR to possibly IFR
conditions may be possible at times especially with any heavier
showers. Precipitation will be possible at KJAC through the
overnight with temperatures likely at or slightly above freezing
leading to a mix of rain/snow or all rain. Showers should gradually
dissipate by the late morning hours on Wednesday. The other
terminals that may see an isolated brief shower or two are KCOD,
KPNA, KCPR, and KWRL. Most of these terminals have low chances, less
than 30% for a shower with possibly better chances at KCOD Wednesday
morning. The other main concern will be strong gusty winds of 35 to
45 knots at KCOD, KCPR, and KRKS. These winds are expected to
persist for another 2 or 3 hours after the start of the period
before weakening. Winds will return to these terminals once again
Wednesday morning with 30 to 40 knots possible through the end of
the period. All other terminals are not forecast to see as strong of
winds but gusty conditions will still be possible at times.
Widespread gusts of 25 to 35 knots are possible at or shortly
after the start of the period with these winds weakening after
sunset with breezy conditions lingering. Mountain obscuration
will likely persist through all of the TAF period with some
improvement possible near the end of the period.

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-
012.

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

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.

&&

$$

UPDATE...McDonald
DISCUSSION...Straub
AVIATION...Dziewaltowski