991
FXUS65 KCYS 231107
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
407 AM MST Sun Nov 23 2025

.KEY MESSAGES...

- The next storm system moves towards the region today,
  increasing precipitation chances across the western Nebraska
  Panhandle.

- A secondary system will move through Monday into Tuesday,
  bringing a strong cold front and very cold temperatures.

- Models still agree on a potential arctic front moving into the
  region late this week into the weekend. Very cold temperatures
  and accumulating snowfall remain possible.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 104 AM MST Sun Nov 23 2025

Clear skies across most of the CWA tonight as temperatures drop into
the 20s and 30s. GOES-19 Nighttime Microphysics shows some upper-
level clouds beginning to intrude on Carbon County as a result of
the next incoming system currently near the Four Corners region
tonight. Clouds will continue increase through the morning hours as
this system approaches, though most locations should remain clear
through sunrise.

The next system expected to impact the CWA will slowly move
northeasterly today, with increasing clouds aloft. The closed low at
250mb looks to remain just south of the CWA for much of the day
today before weakening slightly into an open wave by Monday morning.
The overall vertical structure of this system is good, with a mostly
stacked system throughout the atmosphere. The 700mb low will move
across the Rockies this morning/afternoon before strengthening to
the east. This low will meander more southeasterly than due
easterly, leading to limited precipitation impacts across the CWA.
The best chance for precipitation will be wrap-around moisture
across the western Nebraska Panhandle, names Kimball and Cheyenne
counties, before the low moves off and precipitation chances come to
an end. The system looks to remain fairly warm, leading to
precipitation primarily falling as rain, with the potential for the
western most edge of the precipitation to see a brief rain/snow mix.
Surface temperatures will remain in the 40s and 50s across the
region, with the chance for portions of the Nebraska Panhandle to
see 60F, further supporting rain rather than snow with this system.

Behind the departing system on Monday, upper-level flow will briefly
favor ridging before the next, and potentially more impactful, upper-
level trough pushes into the region. The CWA will largely be near
the base of the upper-level trough, with a 700mb trough diving down
into the northern CONUS from southern Canada. This trough will be
impactful in two separate ways: strong winds in the wind prones and
very cold temperatures moving in. As the 700mb trough dives into the
CONUS, 700mb height gradients strengthen across the CWA, leading to
a 700mb jet of 50 to 55kts Monday afternoon/evening. GFS omega
fields suggest strong downward omega values east of the Laramie
Range as well as a mountain wave signature west of the Laramie
Range. Therefore, strong winds are expected to mix down to the
surface, with in-house guidance suggesting 60 to 65% probability of
high winds at Arlington/Elk Mountain and Bordeaux. A brief increase
in both 700mb winds and downward omega values favor a significant
peak in wind speeds at the I-80 Summit and potentially spreading
eastward into the South Laramie Range Foothills zone. As a result, a
High Wind Watch has been issued for Arlington/Elk Mountains,
Bordeaux, the I-80 Summit, and the South Laramie Range Foothills
from 15Z Monday through 09Z Tuesday. With this system a chance for
precipitation is expected across northern zones as the cold front
begins to push into the region. 700mb temperatures are progged to
tank into the -12 to -10C range by Tuesday morning, leading to a
very cold start to the day Tuesday. See the long term discussion for
more details on this approaching front, as well as the secondary
cold snap anticipated late this week into the weekend.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 245 PM MST Sat Nov 22 2025

A brief taster of wintry temperatures is on track for Tuesday. A
strong but fast moving Pacific cold front will be clear through the
area by Tuesday morning, leaving much colder temperatures and breezy
northwest winds. 700-mb temperatures plummet to around -10C to -14C
behind the front, which is not too unusual for this time of year,
but may feel chillier coming off of what has been an exceptionally
warm November so far. Highs will largely be in the upper 20s to 30s
with wind chills in the teens and 20s as a result of gusty northwest
winds. Unfortunately for our near record low mountain snowpack, this
system does not appear likely to bring much snowfall. Light snow
showers are favored into Tuesday morning for our northern zones and
southern mountains, but QPF scenarios are unimpressive. Even the
90th percentile snowfall remains at a fairly dismal 0.25" of liquid
for the higher peaks of the Sierra Madre and Snowy ranges. Average
SWE deficits compared to median in each range are nearly ten times
that.

This system will race off to the east by Wednesday, leaving a
northwest flow pattern over the Rockies as ridging tries to expand
back to the east. A powerful jet stream is expected to round the top
of this ridge, with a decent amount of Pacific moisture embedded.
Exactly where this moisture plume sets up will determine if light
mountain snow chances continue Wednesday into Thursday, or if we dry
out once again and remain so into the Thanksgiving holiday. GEFS
members generally show the ridge expanding just a little faster,
enough to shunt the moisture plume away from our mountains, but
ECMWF members tend to keep light snow in the southern Wyoming
mountains into Thanksgiving Day. Low end PoPs and minimal QPF are
retained in the official forecast for the mountains. Precipitation
can`t quite be ruled out for populated areas Wednesday into early
Thursday, but with only about 10 to 15% of members showing anything
at all, PoPs are below slight chance at this time. Regardless of the
precipitation outcome, our position under the right exit region of a
strong jet aloft will favor descent and thus at least elevated wind
speeds returning after a brief lull late Tuesday into early
Wednesday. An early look into high wind parameters suggests a fairly
unimpressive MSLP gradient across the barrier, but decent 700-mb
wind speeds and height gradients. This tends to point more towards
an Arlington/Elk Mountain event rather than something for all wind
prone areas, but there is plenty of time for this to change. For
now, winds were increased slightly over NBM guidance but are
currently below high wind thresholds. Look for a return of near to
slightly above average temperatures for Thursday and Friday across
the area as 700-mb temperatures recover to near 0C for the period. A
cold surface high over the plains may keep an inversion over
northern or eastern portions of the area and cap temperatures below
the potential exhibited by these values aloft, but this is a little
too much detail to get into at this lead time.

At the very end of the operational forecast period, ensembles
continue to display unusually strong consistency in another major
cold front. There is disparity in the strength and timing of this
event, as well as how much snowfall might accompany this front, but
confidence is fairly high (relative to typical day 8+ forecasts) in
a major change to colder temperatures beginning around Saturday or
Sunday. Ensemble median 700-mb temperatures fall to -12C at KCYS and
-15C at KDGW, with nearly all members dropping temperatures below
average by Sunday. The vast majority of members also have light to
moderate snow falling across most of the area, which is again quite
unusual for this lead time. 75% of members have widespread 1" or
more of snowfall. A major snowstorm does not appear particularly
likely, but there is fairly good confidence in some form of a light
to moderate snowfall event between Saturday 11/29 and Monday 12/1.
Since this coincides with a busy period of travel across the
country, it is worth some early discussion here. We will continue to
monitor this over the week ahead.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 407 AM MST Sun Nov 23 2025

VFR conditions expected through the majority of the 12Z TAF period.
Some upper-level clouds are slowly moving in to KRWL, KLAR, KCYS,
KSNY, and KBFF, and will continue to spread northerly through the
morning hours. Mostly light winds today with mid-level clouds
present at all terminals. KSNY will see lowering ceilings and
increasing precipitation chances after sunset with MVFR to IFR
conditions possible late in the period.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Watch from Monday morning through late Monday night
     for WYZ106-110-116-117.
NE...None.

&&

$$

SHORT TERM...AM
LONG TERM...MN
AVIATION...AM