124
FXUS65 KCYS 011201
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
500 AM MST Mon Dec 1 2025

.KEY MESSAGES...

- A High Wind Warning has been issued for the wind prone areas
  of southeast Wyoming beginning Monday evening and continuing
  through noon Tuesday.

- Long term remains active with multiple systems promoting
  prolonged periods of high winds alongside mountain snow and
  chances of lower elevation snow as well.

- Temperatures will remain very cold through mid-week, before a
  weak warming trend arrives Wednesday onwards.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 255 AM MST Mon Dec 1 2025

Current IR Satellite loop shows the upper level trough
responsible for the light snow on Sunday moving eastward with
the trough axis near the Colorado/Wyoming/Nebraska border at
this hour. Light snow has either ended or tapered to brief snow
flurries early this morning with no additional snow accumulation
expected. Therefore, cancelled the Winter Weather Advisory for
the mountains with most locations showing between 4 to 7 inches.
Very cold temperatures remain over the area with readings in the
single digits to low teens for most places. A few below zero
readings are starting to show up, but temperatures will likely
not fall too much more with increasing westerly winds and some
patchy fog in the more sheltered valleys. Once the upper level
system ejects eastward, it should pull most of the arctic
airmass with it as 700mb temperatures increase above -10c. High
temperatures today will likely climb above freezing for some
areas, especially far southeast Wyoming and western Nebraska.

Main forecast concern over the next 36 hours is locally strong
winds over the wind prone areas...bringing some concern for
blowing snow in addition to wind gusts around 70 MPH. Models
show another disturbance quickly digging south into the Pacific
NW, Idaho, and Montana late this afternoon and tonight. This
system will include a strengthening upper level as it moves
southeast as the arctic airmass retreats eastward. All models
show low to midlevel pressure gradients quickly responding with
increasing 700mb subsidence along the spine of the mountains.
The GFS, NAM, and Canadian continue to show 700mb winds increasing
to 65 knots by early Tuesday morning. Models appear to have
leveled off with these winds speeds with very little chance from
24 hours ago. In-house wind guidance continues the upward trend
with probabilities...now nearing 90% to 95%. Guidance is also
showing higher probs for the central and southern Laramie
Range...up to 70%. With growing confidence, upgraded the High
Wind Watch to a Warning. Decided to start the Arlington/Elk
Mountain zone early and closer to 2 PM with most models showing
an earlier trend for gusts over 50 MPH during the day. Smaller
timing window for Bordeaux and the I-80 Summit, but after
looking at recent data, may need to extend the I-80 Summit
through Tuesday afternoon. Will let the next shift(s) take
another look at it though before making any adjustments.

Otherwise, kept blowing snow in the forecast for portions of
I-80. However, won`t have any current surface snow depth
observations for another 4 hours, so confidence is limited at
this time. With the increasing winds, and breezy conditions
outside the wind prone areas, temperatures tonight won`t be as
cold with lows generally in the teens to low 20s.

For Tuesday, strong winds will continue for the wind prone areas
with breezy conditions elsewhere as the upper level disturbance
across the PAC northwest becomes a broad upper level trough as
it digs southeast into Wyoming and Utah. With increasing
westerly downslope winds and "warmish" air out ahead of the
trough, expect temperatures to respond with a brief warming
trend as highs return to the mid 30s (west) to mid 40s (east).
This will help settle the snowpack with diminishing blowing snow
concerns once we get into late Tuesday morning.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 300 AM MST Mon Dec 1 2025

Long term forecast remains on track. Edited previous discussion
to take out mention of Tuesday`s high wind event (see short term
discussion). Otherwise, another light snow event, similar to
the previous two this past weekend, is still on track for
Tuesday night and Wednesday. Models have trended a little
further south with this system, but the I-25 corridor and areas
west of I-25 still look like they`ll receive another few inches
of snow with this system. The 00z ECMWF has backed off on the
slower solution, but 33% of it`s ensemble members still show
0.20+ QPF. Otherwise, a progressive northwesterly flow pattern
is expected past midweek...which typically leads to increasing
winds across the area, several chances for mountain snow, and
even some low elevation snow...especially across southeast
Wyoming Friday night and Saturday.



Previous discussion...
Issued at 339 PM MST Sun Nov 30 2025

Long term remains active thanks to multiple systems bringing
rounds of precipitation alongside long durations of high winds,
with temperatures steadily warming during the later part of the
week to bring us back to near normal by the weekend.

Meanwhile a few models have shown some increased QPF which
would lead to higher snowfall late Tuesday and into Wednesday,
but the majority of ensembles and the NBM are keeping QPF in the
mountains and to our south, so the expectation remains we`ll
see amounts high enough to warrant products, at least
advisories, in the mountains, with around 1-3 inches in the
lower terrain thanks to shadowing effects.

Moving into Wednesday and Thursday, both days should be
relatively calm and dry as the ridge tries to build in, but our
winds will once again begin increasing on Thursday in response
to the next approaching system as pressure gradients tighten and
the 700mb jet begins to re-establish and remain firmly planted
over the CWA through the weekend. In house guidance continues to
highlight this period and with such consistency there is
moderate to high confidence in a multi-day high wind event once
again for our wind prone regions. Meanwhile models expect that
this flow should allow for more chances of mountain snowfall
with some of this able to spill over into the adjacent high
plains, but once again shadowing effects are likely going to
limit how much accumulation we can produce outside of the high
terrain. Finally our temperatures start off near normal on
Tuesday with highs in the 30`s to 40`s, dropping notably on
Wednesday thanks to the passage of the front with the first
system and highs not making it out of freezing, but as the
ridge tries to take control through the weekend a modest warming
trend should bring us back to the 30`s and 40`s by Saturday.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 500 AM MST Mon Dec 1 2025

Upper level trough, which brought snow to most of the region on
Sunday, will continue moving east into the Great Plains today. The
next system will be quick to follow and is forecast to impact the
region late tonight with increasing cloudiness.

HAZARDS/WEATHER TRENDS: VFR will prevail after 14z for all terminals
with breezy conditions expected after 16z. Some patchy fog and/or
low CIGS are possible between now and 14z for the western Nebraska
terminals, but confidence and areal coverage are low enough to not
include in the TAF. Any IFR VIS and CIG will be brief and expected
to lift shortly after sunrise.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning from 8 PM this evening to noon MST Tuesday
     for WYZ106-116-117.
     High Wind Warning from 2 PM this afternoon to 8 PM MST Tuesday
     for WYZ110.
NE...None.

&&

$$

SHORT TERM...TJT
LONG TERM...CG/TJT
AVIATION...TJT