168
FXUS65 KCYS 032135
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
235 PM MST Wed Dec 3 2025

.KEY MESSAGES...

- Winds will pick up again Thursday morning in the wind prone
  areas. Another round of High Wind Warnings have been issued.

- Areas of blowing snow Thursday may impact travel conditions
  in the wind prone areas of southeast Wyoming.

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

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 245 PM MST Wed Dec 3 2025

Last night`s storm system is on its way out today, with radar
showing fairly minimal snow shower activity mainly confined to the
area along the CO border. Satellite imagery shows low cloud cover
beginning to break up as a drier airmass works its way into the
area. Expect skies to clear fully this evening, but this may allow
for a window of radiative cooling to push areas of patchy fog and/or
low clouds back into portions of the area. Confidence is not
particularly high in fog development, but we will need to keep an
eye on this into Thursday morning. With mainly clear skies, fairly
light winds, and some fresh snow cover, temperatures were dropped
several degrees below guidance in the typical colder valley spots,
such as Laramie and Saratoga. If winds pick up faster, or if these
areas develop fog quickly, we may not get quite so cold.

Attention will quickly shift back to yet another wind event on
Thursday morning. Surface high pressure will build into the interior
Rockies while pressure falls over the High Plains tonight,
increasing the MSLP gradient across our mountain barriers. In
addition, a weak shortwave passing to our north will bump up 700-mb
height gradients as it passes nearby. In-house guidance is rather
aggressive, showing nearly 80% probabilities for high winds along
the I-80 wind prone areas. This should be taken with the caveat that
the tool is based on the GFS, which has the strongest pressure
gradients of any global model. While various wind parameters are
less impressive in other models such as the NAM and the ECMWF, they
are still marginally supporting of strong to high winds. Therefore,
there was enough confidence to issue another High Wind Warning,
focusing on only the gap wind areas since this appears to be
primarily a surface driven wind event. This will likely come in two
phases, but there was not enough confidence in the timing or
duration of the potential low to split into two separate warnings.
The first favorable period is Thursday morning when an initial
shortwave trough passes to the north. The 700-mb height gradient
relaxes slightly Thursday afternoon, while the surface high
pressure over the interior Rockies also weakens with its typical
diurnal cycle, briefly reducing the MSLP gradient. Both of
these trends should reverse quickly after sundown Thursday, with
the Thursday night period actually showing the best signal for
strong to high winds. The second period Thursday night may also
send off a few mountain waves closer to the I-25 corridor, but
high wind criteria is fairly low probability at this time (about
20%). In addition to the winds, the higher elevations of I-80
received several inches of snow this morning. Without much time
to crust over, blowing snow could be an issue for travel between
Cheyenne and Rawlins. This was introduced into the official
forecast and is messaged within the High Wind Warning. It is
uncertain whether the blowing snow will be enough to cause
significant visibility reductions, but slick conditions
extending into Thursday look probable. The Bordeaux area (and
all of I-25 between about Chugwater and Glendo) received very
little snowfall this morning, so that warning does not include
blowing snow messaging. However, portions of WY-34 across the
central Laramie Range could see some areas of blowing snow.
Moisture embedded in the northwest flow aloft will also increase
quickly Thursday night, promoting moist upslope flow into the
higher mountain peaks of southeast Wyoming. Look for orographic
snowfall to resume Thursday night into Friday. This will likely
continue for several more days too, but we`ll hold off on any
headlines until it gets a little closer to get some finer detail
on timing and any potential breaks within the period.
Elsewhere, look for seasonable temperatures and breezy
conditions Friday.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Issued at 245 PM MST Wed Dec 3 2025

Ensemble clusters continue to depict northwest flow across the
central and northern Rockies through next week with slight
variations in the zonal vs meridional component by early next week.
Overall with ridging centered over or just offshore southern
California and dominant troughing in the Canadian Maritimes it does
not look to be a particularly amplified pattern the next several
days with low amplitude shortwaves keeping active precipitation
chances in the mountains which occasionally spill into the adjacent
zones and high plains through the period. Temperatures will
gradually warm through the end of the period with highs on the front
range and NE panhandle reaching into the 50s early next week. Most
notably through the extended will be periods of high to very high
winds especially early next week.

- Snow Chances

The high elevation snow that starts on Friday in the Snowy and
Sierra Madre ranges will continue through the weekend with the bulk
of the snowfall coming on Saturday and tapering off on Sunday.
Elevations above 7000ft in the Sierra and 8000ft in the Snowy can
expect greater than 6" from Friday to Sunday and 1-3 feet for areas
over 9000ft elevation. A few more weak shortwaves then rotate
through the northwest flow later in the period bringing more chances
for light snow to the higher elevations but the snow shadow should
be in effect for the front range with only a dusting expected
through the extended period.

- Wind, Wind, and More Wind

Breezy for some of the high elevations on Saturday though not sold
on high wind criteria just yet as in house guidance shows things
improving markedly from the high wind warning that is in effect from
Thursday morning into Friday morning. Currently looking at a 20-40%
chance for high wind criteria for that Saturday surge. Looking
further ahead to early next week 700mb flow of 50-60 kts and as high
as 70-75 kts combined with deeply negative omega will bring strong
winds to the surface early next week. Ensembles certainly support
this with mean gusts ranging from 50-60 mph on the low end for the
wind prone areas with this being another long duration event lasting
from Monday well into the heart of next week. There is even a
greater than 30% chance that lower elevation areas on the front
range like Cheyenne proper get in on the fun by Tuesday.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1043 AM MST Wed Dec 3 2025

Snow will gradually taper off over the next few hours at KCYS
and KLAR, with a few snow showers possible near KCDR. CIGs will
remain MVFR through much of the afternoon, but should begin to
improve by the mid to late afternoon hours. Overnight, we should
start out with mostly clear skies, but there is potential for
some surface fog and/or low CIGs to develop at most terminals.
Confidence in this potential is fairly low at this time. Any
reduction in flight category should end early Thursday morning
when winds flip to westerly.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning from 6 AM Thursday to 6 AM MST Friday for
     WYZ106.
     High Wind Warning from 6 AM Thursday to noon MST Friday for
     WYZ110-116.
NE...None.

&&

$$

SHORT TERM...MN
LONG TERM...TT
AVIATION...MN