127
FXUS65 KCYS 161756
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1056 AM MST Sun Nov 16 2025

.KEY MESSAGES...

- A Pacific storm system will move into the area later this
  weekend bringing snow...rain...and cooler temperatures by
  Monday.

- Gradual cooling trend expected next week with a chance of rain
  and/or snow Thursday and Friday.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 325 AM MST Sun Nov 16 2025

Quiet and dry weather will continue one more day before the next
Pacific storm system impacts the region by late this evening
and tonight. Models show the high amplitude upper level ridge
axis sliding northeast over the Front Range this afternoon and
then east of the area tonight. Current IR Satellite loops shows
the potent upper level disturbance across central/southern
California lifting northeast into the Great Basin region today.
This system is forecast to (finally) give us some precipitation
late tonight through Monday evening across most of the region.
For today, high temperatures will remain in the upper 50s to
upper 60s...warmest across eastern Wyoming and western Nebraska.
Dry conditions will continue until late this afternoon as the
leading edge of the precipitation shield moves into the far
southern Wyoming mountains around sunset.

All models in good agreement as this Pacific storm system ejects
northeast across the area. This storm is trending slower
compared to 24 hours ago and is now keeping a closed low,
instead of the open wave trough, as it redevelops over far
southeast Wyoming and the southern Nebraska Panhandle by Monday
afternoon. This trend has led to poor run to run consistency
between model runs (00z versus 18z, etc), so forecast confidence
is only moderate at best. Thankfully, the storm is pretty
progressive...but will have to watch for any slow down in
forward speed which may exacerbate snowfall concerns across the
high valleys and mountains.

By this evening, negatively tilted trough axis will quickly move
into northern Colorado and eventually southern Wyoming.
Precipitation type will initially begin as rain or rain/snow
mix, even for the mountains, as 700mb temperatures finally fall
below freezing after sunset. There is also some concern of
thunderstorm activity out ahead of the surface cold front. High
res guidance prog reflectivity shows higher DBZ echoes across
Carbon and even Albany county this evening. Believe high res
models are picking up on some conditional instability in the
midlevels as colder air aloft pushes into the area. CAPE values
are generally below 300 j/kg, but it should be enough for some
lines of thunder showers given the amounts of forcing associated
with this system. Added thunderstorms to the forecast, but did
not go as far east as the HRRR suggests given the relatively dry
boundary layer over the eastern high plains. Any rainfall with
quickly change over the snow in the mountains, with snowlevels
falling to 6500 to 7500 feet. All models have increased QPF in
the mountains and adjacent foothills near the Sierra Madre and
Snowy Range. This makes sense given the recent model trend of a
more organized storm system and enhanced west to southwest
upslope flow along the spine of the mountains. Issued a Winter
Weather Advisory for the Sierra Madre Range and the Snowy Range
starting at 800 PM this evening and continuing through Monday
evening. Expect the advisory amounts to be mainly confined to
areas above 8000 to 8500 feet. Thought about issuing a Winter
Storm Watch, but with the bare ground across the midslopes
combined with relatively warm ground temperatures...decided
against it. Will keep an eye on SNOTEL observations tonight
before any potential upgrades. In addition, expect a lull in the
snowfall between the initial convective band this evening and
the upslope wrap-around snowfall tonight after midnight. These
elements should limited rapid snowfall accumulations for most
areas. Will have to monitor the Elk Mountain/Arlington area and
southwest Carbon county for Winter Weather Advisory conditions
as well since models have trended higher with snowfall totals in
these areas. Further east across the high plains, expect some
rain/snow mix down to 6000 feet, but it should mainly be a rain
event for eastern Wyoming and western Nebraska. May need to add
isolated thunderstorms over these areas if model trends
continue.

The biggest forecast uncertainty for this event is winds, likely
due to the change in track and evolution of the storm system.
In-house wind guidance has started to back off with strong winds
across the wind prone areas and sub-wind prone areas along and
west of the Interstate 25 corridor. Models, including some high
res guidance, has completely backed off with the strong wind
potential late tonight, but is now showing the stronger winds
behind the main system during the day on Monday. With so many
uncertainties with timing and track, decided against issuing any
High Wind Watches for now with huge ensemble spreads with
sustained winds and wind gusts. Would like to note that the 00z
NAM and HRRR were the most aggressive with these winds on
Monday, showing gusts up to 70 mph for the wind prone areas and
Cheyenne. These models have since backed off, but still show
very windy conditions. Increased winds a bit, but kept them near
or below High Wind criteria. Another issue is precipitation
loading. With higher snowfall rates expected across the I-80
Summit and Arlington/Elk Mountain compared to yesterday, wind
speeds tend not to be as high as models suggest...especially in
the absence of a developing low pressure system near the
surface.

Otherwise, Monday will be around 10 to 15 degrees cooler as the
long term cooling trend begins. Highs in the mid 40s to mid 50s
are expected with 20s and low 30s in the mountains. Seasonably
cold temperatures expected Monday night.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 310 PM MST Sat Nov 15 2025

A brief ridge sets up Tuesday night into Wednesday, however
another system pushes into the Western coast Wednesday night.
Cluster Analysis shows some uncertainty with the location and
strength of the next system. Some clusters show a potential for
the system to track to the northeast from the California coast
allowing for the system to become negatively tilted as it tracks
through the Intermountain West to give us daily precipitation
chances through the weekend. The other clusters depict a more
eastern track from the California coast. This track amplifies a
ridge over the Intermountain West as the system would then
traverse the southern portion of the United States. If this
ridge sets up it would decrease the precipitation chances in the
back half of the week extending through the weekend.

The global ensembles have also reached a consensus of the gradual
downward trend in the daily high temperatures. Colder air spills
down from the Canadian Providences following the low pressure
systems moving through the upcoming week. 700mb temperatures are
expected to hover around -4c for this upcoming week. This will
gradually drop temperatures from the 60`s at the start of the week
into the 40`s by the weekend. Overnight temperatures also look to
ride the downward trend with temperatures reaching into the 20`s by
next weekend. Ensembles do show the downward temperature trend
continuing to the end of the month. By the end of the month high
temperatures could be in 20`s and 30`s with overnight temperatures
in the teens if this trend continues.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1055 AM MST Sun Nov 16 2025

Minimal aviation concerns are expected during the day at all
terminals. This evening, a storm system will begin to move into
southeast Wyoming, bringing precipitation and low stratus. A rain
snow mix will be possible at KRWL and KLAR, likely reducing
visibility below VFR criteria. Low stratus will also lead to low
CIGs at KRWL. Precipitation will move into terminals further
east later overnight and into Monday morning, however this
precipitation will likely remain as rain, causing less impacts.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory from 8 PM this evening to 8 PM MST
     Monday for WYZ112-114.
NE...None.

&&

$$

SHORT TERM...TJT
LONG TERM...MM
AVIATION...SF