346
FXUS65 KCYS 181157
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
510 AM MST Tue Nov 18 2025

.KEY MESSAGES...

- Seasonable temperatures and mostly dry weather expected
  through Wednesday night. Mountain snow showers possible each
  day.

- Models continue to alternate on the strength and placement of
  a low later this week, but expecting at least some
  precipitation and snow with this system, mainly south of the
  North Platte River Valley.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 230 AM MST Tue Nov 18 2025

Upper level storm system which brought some snow, rain showers,
and wind to the region is now accelerating eastward into the
Missouri River Valley at this hour. Winds have quickly decreased
across southeast Wyoming in the last few hours and radar shows
diminish rain/snow shower coverage. Removed POP after 300 AM,
but expect clouds to remain over the region. All headlines have
expired on time yesterday evening.

Models in good agreement for Tuesday and Wednesday, showing a
short wave ridge axis quickly moving into the Front Range and
east of the Front Range by late tonight. A slight warming trend
is expected with partly sunny or mostly cloudy skies and dry
weather. Can`t rule out some off/on snow showers for the
mountains due to orographic lift and a little conditional
instability, but accumulations should remain less than an
inch. 700mb temperatures will increase to near 0c, which
translates to afternoon temperatures peaking in the upper 40s
to upper 50s for most of the area, and low 60s possible for the
lower elevations of western Nebraska. Periods of mostly cloudy
or cloudy skies are expected due to some low to midlevel
moisture and jet stream influence. This will likely keep low
temperatures from becoming too cold each night with overnight
temperatures in the mid 20s to mid 30s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Issued at 215 AM MST Tue Nov 18 2025

Made a few minor updates regarding the storm system on Thursday
and Friday. Ensemble guidance continues to show a chance for a
widespread precip event with even some snow across portions of
the area. Model soundings have trended a little more aggressive
with an isothermal layer in the lowest 3000 feet due to
increasing east to southeast upslope winds as the main storm
will likely redevelop across eastern Colorado or western
Kansas/Oklahoma panhandle region. How this storm system moves
and evolves after this redevelopment will mean the difference
between foggy conditions and a little drizzle...or heavy wet
snowfall along the I-80 corridor down to elevations of 5000
feet. In addition, if the secondary storm along the Pacific
coastline digs further south quicker...allowing the storm to our
south to eject northeast instead of eastward, we could see a
Colorado low type scenario. A lot of questions still remain
with this storm, but ensemble guidance now has around half it`s
members showing between 0.25 to as high as 0.85 liquid south of
the North Platte River valley. There likely won`t be any impacts
well north of Interstate 80, but can`t even rule that out with
current ensemble spreads.

For now, lowered temperatures...especially on Friday with cloudy
skies and easterly winds. Increased POP a little above the NBM,
but believe the NBM POP has a pretty good handle on this system.
This will have to be watched closely over the next few days
since models tend to struggle with resolving (two) closed low
pressure systems.

Previous Discussion...
Issued at 256 PM MST Mon Nov 17 2025

The long term is an unsettled pattern that will see our
temperatures dropping closer to normal but then ultimately
warming again as a closed upper low makes its way across the
region that models have been waffling over, leading to
uncertainty in how significant of impacts will occur from this
system to end the week. Wednesday night begins under transient
ridging that will continue into early Thursday, but by the
afternoon and evening an approaching closed low will bring
precipitation and unsettled conditions back to the region. There
is a large amount of uncertainty with this system though as
models are unable to come to an agreement on the strength and
track of this low from run to run. The latest 12Z guidance is
less impressive in terms of precipitation for the CWA, as both
the ECMWF Ens and the GEFS show limited wintry accumulations in
both the mountains and even adjacent valleys and high plains due
to a more southerly track of the system. Nonetheless, both are
still showing at least some accumulation even down into Cheyenne
proper possible before temperatures jump back above freezing on
Friday, so look for at least a non-zero chance that we could
see a little bit of snow for the mountains and portions of
southeastern Wyoming before this system departs. On the note of
temperatures, highs on Thursday should drop into the 40`s to
50`s, with temperatures cooling a few degrees further on Friday
as we see low 40`s for highs in a few locations, particularly
along the I-80 corridor where the most likely impacts from the
low will be possible. Moving into the weekend another transient
ridge should briefly "warm" us back up with 40`s to upper 50`s
expected, warmest east of the Laramie Range, but by late Sunday
the next impactful system will be on our doorstep with more
precipitation and cooling temperatures possible.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 455 AM MST Tue Nov 18 2025

Upper level low, which brought some rain, snow, and wind to the
region on Monday, will continue to push east into the Great Plains
today. Although it will remain partly to mostly cloudy, dry
conditions are expected this afternoon and into this evening.

HAZARDS/WEATHER TRENDS: IFR to LIFR conditions will continue for
KCDR and KAIA this morning with low CIGS and patchy fog. Light
surface winds and low level moisture should remain in place, so do
not expect the fog/stratus to lift until midday. Kept IFR conditions
at both these locations until 19z to 20z, with the stratus/fog
slowly lifting after sunrise. VFR conditions expected for all
southeast Wyoming terminals, KBFF, and KSNY through the forecast
period.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.

&&

$$

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