289
FXUS65 KRIW 231754
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1054 AM MST Mon Dec 23 2024

.KEY MESSAGES...

- Light snow continues across the west through Monday afternoon.
  Snowfall rates increase slightly this morning. Winter travel
  conditions expected, especially over mountains passes.

- Another system arrives Tuesday night, bringing light snow
  chances to western portions of the forecast area on Christmas.

&&

.DISCUSSION...
Issued at 1216 AM MST Mon Dec 23 2024

A weak, elongated trough will approach the Cowboy State today,
bringing another round of light to moderate snow to the western
mountains through the day. Snowfall amounts will be highest over the
Tetons and the Pitchstone Plateau in Yellowstone NP, with 8 to 12
inches expected. Locally higher amounts around 16 inches will occur
on the higher peaks. Lesser amounts of 4 to 6 inches is expected
over the western mountains, with 2 to 4 inches on Togwotee Pass.
Conditions will remain dry with slightly above normal temperatures
east of the Divide. Winds will be gusty across the south, including
the Casper area, with gusts of 25 to 30 mph.

Snow will end later this evening, as a ridge transitions over the
region. Dry conditions and above normal temperatures (at least east
of the Divide) will continue. Gusty winds will be confined to the
Wind Corridor, with gusts of 25 to 35 mph.

The odds for a White Christmas is not looking good for much of the
forecast area. The closed low that has been forecasted for the last
several days remains on track to dive southward over the Four
Corners region Tuesday night into Christmas Day. However, a trough
that is in phase with the low will move over the Northern Rockies.
This will bring light snow to western portions late Tuesday night
and through Christmas morning. This could even include Green
River/Rock Springs. Amounts will generally stay under an inch, with
the mountains possibly picking up 2 inches.

Conditions will remain relatively quiet Thursday and Friday, with
light snow remaining possible over the western mountains. A more
active pattern looks to develop by the weekend, with snow continuing
over the west and gusty winds for much of the area.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1055 AM MST Mon Dec 23 2024

West of the Divide (KBPI, KJAC, KPNA, and KRKS) Terminals:

A weak shortwave trough continues to move from Idaho into
Wyoming today, primarily bringing snow to western-central WY
with scattered showers to other areas. KJAC has dropped to IFR
conditions with the initial push this morning. Should improve to
MVFR this afternoon, with a chance of IFR at times as heavier
snow showers move through the area. Models are indicating
improving conditions after 24/00Z with lingering showers through
the evening. KBPI and KPNA should also see snow showers (MVFR) at
times this afternoon and early evening before improving by
24/06Z. Gusty west winds will also continue this afternoon at
KRKS with a lesser chance of snow showers late in the afternoon
and early in the evening before improving by 24/06Z as well.

After the system moves through by 24/06Z, and shortwave ridge
will move in with mid- and high-level clouds. Indications are
pretty good for some fog late in the night and early in the
morning for the Upper Green River Basin (KBPI/KPNA). There is a
low chance of fog around KJAC due to the thicker cloud cover
overnight, but the possibility still exists.

VFR conditions should prevail for most of the day Tuesday across
western WY with the high pressure. Moisture increase again
Tuesday evening with the next system bringing snow to western WY
early Wednesday morning.

East of the Divide (KCOD, KCPR, KLND, KRIW, and KWRL) Terminals:

A shortwave trough in westerly flow is impacting Wyoming today,
with snow across the west, and cloudy conditions east of the
divide. A few areas may see some snow showers later in the
afternoon and early in the evening as a result, with KCPR having
the best chance during the evening hours before 24/06Z. VFR
conditions should persist, but local MVFR conditions are
possible under the snow showers. Breezy conditions will continue
at KCPR for a few more hours, then decrease before sunset. Gusty
west winds are a 50/50 for KCOD also for a few hours before NE
winds develop. Typical overnight flow are expected after 24/06Z
as high pressure move over the area Tuesday morning. KCPR will
return to breezy and gusty SW wind around 24/16Z.

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 until 7 PM MST this evening for WYZ012.

&&

$$

DISCUSSION...LaVoie
AVIATION...McDonald