634
FXUS65 KCYS 290751
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
151 AM MDT Thu Oct 29 2026

.KEY MESSAGES...

- Dry, warm, and breezy conditions are expected to continue
  through Thursday, with mild overnight lows.

- Chances for a few showers return Saturday (Halloween) with
  temperatures remaining mild.

- A pattern change to colder, wetter, and windier conditions is
  favored Sunday into Tuesday, but the details remain highly
  uncertain at this time.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 151 AM MDT Thu Oct 29 2026

A fairly quiet end to the work week is expected across southeast
Wyoming and western Nebraska. Upper-level flow will remain
southwesterly throughout the day Thursday and Friday as an upper-
level trough strengthens off the West Coast and a ridge builds
across the central CONUS. Weak 700mb flow develops with the building
ridge, with temperatures increasing into the 3 to 5C range
throughout the afternoon Thursday. Surface temperatures are expected
to warm to the upper-50s to mid-60s across the region with no
precipitation expected at this time. Overnight lows Thursday into
Friday will drop into the mid-30s to mid-40s, a fairly mild night
for this time of year. Surface winds will remain mostly light,
around 10 to 15 mph, throughout the day Thursday. This will result
in a quite pleasant fall day for much of the area, so be sure to get
outside and enjoy it!

Friday will be another mild day as southwesterly flow remains in
place as the upper-level trough off the coast of the Pacific
Northwest slowly moves inland. A weak, upper-level shortwave is
currently progged to move northeastward out of the Four Corners
region towards the CWA throughout the day Friday. This shortwave
looks to push through the region between 21Z Friday and 03Z
Saturday. This system will be quite weak by the time it reaches the
CWA, with minimal associated 500mb vorticity with the shortwave. The
700mb shortwave will be very diffuse by the time it reaches
southeast Wyoming later Friday evening, however, it should still
provide some weak ascent across portions of the CWA. Weak 700mb warm
air advection with further support some forcing, though it too will
be quite weak. 700mb temperatures will top out around 6C for
portions of the area. With the passing shortwave, there will be a
slight chance for PoPs across the region. Significant precipitation
is not anticipated and all precipitation looks to fall as rain and
not snow, given the warmer 700mb temperatures. High temperatures on
Friday will be in the mid-50s to mid-60s, with the Nebraska
Panhandle likely being the cooler location due to overcast skies for
much of the day. Overnight lows will decrease into the mid-30s to
mid-40s, with the Panhandle remaining warmer due to the increased
cloud coverage across the area.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Issued at 151 AM MDT Thu Oct 29 2026

No major changes. Please see previous discussion...

Most of the area will see pleasant conditions for Halloween trick-or-
treating this year. Broad ridging will remain over the area this
weekend, supporting above average high temperatures ranging from the
upper 50s in Carbon and Albany counties to the low to mid 60s over
the High Plains. Expect a mix of cloud cover and sunshine as
plentiful moisture moves over the area aloft. A weak vort-max
passing through the area in the southwest flow overhead will help to
support a few afternoon and evening showers, mainly over and near
the higher terrain, but the chance for appreciable rainfall or
thunder is low. Due to high humidity and cloud cover, overnight low
temperatures will be mild for this time of year, only dropping to
the upper 30s to lower 40s east of I-25, and mid to upper 30s to the
west. Near saturated conditions will produce the potential for some
spooky fog to develop both Saturday morning and Saturday night.
Sunday looks mild again, but slightly cooler than Saturday with
skies becoming mostly cloudy ahead of the next storm system
approaching the area.

A complex storm system will push across the western CONUS Sunday
into early next week. Two major players will make up this system:
first, a strong, moisture-laden upper level low riding the
subtropical jet stream into the southwest and second, a potent
Pacific trough pushing into the northwest. The primary questions
concerning the evolution of this system are if, when, and where the
two approaching systems might merge together. Ensembles have shifted
slightly over the last 24 hours, but have yet to converge on a
solution. Thus, several scenarios still remain, though the
probabilities have changed. In the first scenario (approx 40%
chance), the two features do not merge at all. Two separate mid-
level circulations competing with one other would mean muddy forcing
forcing for ascent and limited precipitation potential. We could
still expect some rain and snow showers, but amounts would be modest
(0.25" or less for Laramie, Cheyenne, Wheatland, Scottsbluff, 0.25"
to 0.5" in Rawlins and Chadron). In the second scenario (approx 50%
chance), the two systems merge, but this occurs a little too late
and a little too far east for a widespread major precipitation event
for our area. Still, it would be enough for a moderate rain event
over western Nebraska, and some potential for accumulating snow
especially for the elevated ridges (Cheyenne Ridge & Pine Ridge).
The scenario in which the two systems merge early enough to produce
a major event has decreased in probability (to around 10%) as fewer
ensembles now show this potential. The ECMWF Extreme Forecast Index
for QPF today has decreased slightly as well to around 0.5 to 0.6
over much of the area. This tells us that while an anomalous event
is still possible, only a small subset of ensemble members show
this, keeping confidence low.

Overall probabilities for 0.5" of liquid precipitation are the
lowest around Laramie, Cheyenne, and Wheatland (30-40%).
Probabilities increase both east and west, with Rawlins around a 50%
chance to exceed 0.5" and the Sidney to Chadron corridor in the 60
to 70% range. In addition to the uncertainty in QPF, there is also
uncertainty in the snow levels with very marginal temperatures for
snow over much of the area. Cooler air moving in through the event
should lead to snow levels starting fairly high (perhaps 9000 ft)
and then dropping overnight Sunday night and through the day Monday.
The question is how low they can get. Thus, there is fairly good
confidence in accumulating snow for the mountains (90+% chance for
1" and 50% chance for 6"), but lower confidence around where most
folks live. The best chances for 1" or more of snow outside of the
mountains are in the valleys of Carbon and Albany counties, and the
elevated ridges of the High Plains.

Regardless of the precipitation outcome, a cold front will sweep
through the area Sunday night, bringing colder and windier
conditions into the area for Monday. Which of the above scenarios
that ends up playing out will also affect the wind direction and
potential for high winds. Still, there is high confidence in a windy
day along and east of the Laramie range. About 25% of ensemble
members have 700-mb winds sufficiently high to support widespread
high wind potential, while the I-80 summit area has about a 50%
chance for high winds. Look for lingering impacts in the form of
cool temperatures and windy conditions on Tuesday, but we should
start to lose the wind and warm up slightly by Wednesday.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1100 PM MDT Wed Oct 28 2026

No aviation concerns as VFR conditions will prevail across all
terminals for the duration of this TAF period. A few high level
clouds are rolling through, they pose no threat, along with winds
generally less than 10 knots, varying in direction from southerly to
southwesterly.

&&

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

&&

$$

SHORT TERM...AM
LONG TERM...MN/AM
AVIATION...RZ