408
FXUS65 KCYS 022229
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
329 PM MST Tue Dec 2 2025

.KEY MESSAGES...

- Another round of light snow will move through the area this
  evening through Wednesday morning.

- Most areas can expect between a dusting and an inch of snow,
  but a few inches will be possible between Rawlins and
  Cheyenne.

- Long term remains active with multiple systems promoting
  prolonged periods of high winds, light snow and cold but
  steadily warming temperatures.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 330 PM MST Tue Dec 2 2025

Visible satellite imagery shows ample cloud cover across the area
this afternoon, streaming out ahead of a weak upper level shortwave
sagging southward over the northern Rockies. This is associated with
modestly higher surface pressure also moving southward at this hour,
which is beginning to decrease the pressure gradient across the
mountain barrier and thus weaken the wind speeds. High Wind Warnings
should be able to expire on time in a few hours. The surface high
will continue to push south this evening as the shortwave aloft
promotes some modest lift. Other mechanisms for lift will be weak
frontogenesis as the reinforcing cold front pushes up against the
Rockies, along with light, shallow surface upslope flow from north
to northeast winds. While we have a few mechanisms present for lift,
all will be fairly weak, so snowfall rates are expected to be light
as well.

Expect light snow to pick up during the late evening hours
today and last through Wednesday morning, tapering off by noon. Most
of the area can expect between a light dusting and an inch, but
there will likely be some higher amounts between Rawlins and
Cheyenne and points southward. There is still a bit of uncertainty
in this potential. High resolution models are sharply divergent,
with some (e.g. 3km NAM) showing barely a dusting for the entire
forecast area, while others (e.g. HRRR) show a widespread 2 to 4"
along the I-80 corridor. The official forecast sticks close to a
blend of the HREF and the ECMWF ensemble which is an average of both
scenarios. Leaning on the cautious side, we have issued a Winter
Weather Advisory for the higher elevation portions of I-80,
including the Arlington/Elk Mountain areas and the I-80 summit. Both
of these areas can do well in northeasterly upslope. The Laramie
Valley was left out of this expansion of the Winter Weather
Advisory, since the low-level northeast winds may cut down on totals
in the immediate vicinity of the city of Laramie. However, totals
may increase again heading west from the city on the western side of
the valley. While the mountains are still expected to receive some
light snow tonight, totals will likely be on the very low end of
yesterday`s expectations. The first phase of the event with moist
westerly upslope flow essentially failed to materialize today thanks
to some dry air in the mid-levels.

Mostly cloudy skies and a reinforcing shot of cold air will keep
temperatures cold on Wednesday after the snow departs. Highs will
stay stuck in the 20s for most, with breezy north winds in the
morning decreasing as the day goes on. Clouds will clear from
northwest to southeast Wednesday afternoon and evening. With winds
expected to be light initially, decided to nudge the temperature
forecast towards the NBM 25th percentile, and then lowered further
in the typical colder spots of Laramie, Saratoga, and Alliance.
Temperatures tanking below guidance will be contingent on wind
speeds which are expected to creep up in the higher elevations
overnight not mixing down to the valley floors.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Issued at 330 PM MST Tue Dec 2 2025

Long term looks to remain stuck firmly under northwesterly flow
as we see the CWA between high pressure ridging to the
southwest and several small troughs to our north to northeast,
bringing a pattern that will include breezy winds, periods of
precipitation primarily in the mountains but occasionally
spilling into the adjacent zones and high plains, and
temperatures that should very gradually warm through the end of
the period.

Ensemble clusters have been in pretty solid agreement on the
overall pattern, with primary differences lying in the strength
of the features in the long term, and small nuances in how the
ridge or troughs impact one another. Nonetheless, colder
airmasses should remain further north and east of us, allowing
the region to remain at or just below normal through the
weekend, with temperatures then becoming near to just above
normal by early next week. Meanwhile moisture will stream across
our CWA and allow for several days of precipitation that will
primarily be influenced by upslope flow into the the mountains
and produce high terrain snow, but some of this might spill
over into the adjacent valleys and down to the high plains at
times, particularly on Friday into Saturday when moisture will
be highest. Finally the low level jet will be just as active as
you would expect for December, with the 700mb flow averaging
around 50-60 knots for our wind prone locations for almost all
of the long term, and downward omega values favorable to bring
this flow to the surface, likely prompting even more high wind
warnings yet again.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1052 AM MST Tue Dec 2 2025

Breezy conditions expected over the next several hours, though
winds have been under performing at most TAF sites. Still,
expect the potential for winds gusting 15-25 knots before
relaxing later this evening. A system then moves in and brings
lowered cloud decks alongside chances of snow showers, with MVFR
to IFR potential CIGs and VIS, but conditions could locally
deteriorate to LIFR status under heavier snow or even lower
cloud decks.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning until 5 PM MST this afternoon for WYZ106-116-
     117.
     High Wind Warning until 8 PM MST this evening for WYZ110.
     Winter Weather Advisory from 9 PM this evening to 11 AM MST
     Wednesday for WYZ110-116.
     Winter Weather Advisory until 11 AM MST Wednesday for WYZ112-
     114.
NE...None.

&&

$$

SHORT TERM...MN
LONG TERM...CG
AVIATION...CG