Weather alerts for the NWS Cheyenne WY forecast area

000
FXUS65 KCYS 281109
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
509 AM MDT Wed Oct 28 2026

.KEY MESSAGES...

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

- Chances for a few showers return Friday into 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 THURSDAY NIGHT/...
Issued at 150 AM MDT Wed Oct 28 2026

Another relatively quiet night is in store for SE Wyoming and the 
Nebraska Panhandle, with no widespread precipitation expected aside 
from a few light showers that may manage to sneak into northern and 
western portions of Carbon County. These are associated with a weak 
mid-level disturbance that is currently moving across Western 
Wyoming and Utah which can be seen clearly on GOES mid-level water 
vapor imagery. Although most areas will remain dry, did decide to 
increase PoPs mainly for Rawlins and points north and west if a 
shower does decide to sneak into the area. 

Current METARs and web cameras are showing some dense fog across Box 
Butte, Morrill, and Cheyenne Counties in the Nebraska Panhandle, so 
went ahead and included these areas in a Dense Fog Advisory until 
8AM MDT. Will have to monitor trends via satellite imagery across 
the western counties of the Nebraska Panhandle for fog, however 
expecting the most widespread, dense fog to remain east of a 
Scottsbluff to Kimball line. The moist conditions this morning are 
being driven by a weak lee trough which is inducing SE cyclonic 
upslope flow, and is expected to cease into the day as the flow
becomes more out of the west or southwest. As we know, westerly
winds translates to downslope flow in our area, and therefore 
adiabatic warming as the air descends the higher terrain onto 
lower elevations, so we can expect a similarly mild day to 
Tuesday. High temperatures are expected to again stand 5-10 
degrees above average for this time of year, with low to mid 60s
forecast east of the I-25 corridor, and low to mid 50s east of 
the Laramie Range. As for our winds, not expecting as strong of 
winds as we did yesterday over the wind-prone areas along I-80, 
however cannot rule out some gusts of 50-55 mph around sunrise. 
700 mb flow will begin to relax by noon as weak shortwave 
ridging builds across the Northern Rockies. Expect another quiet
night overnight into Thursday underneath the weak ridge, with 
mostly clear skies and generally light winds.

Lows on Thursday morning are still expected to be fairly mild for 
this time of year, with locations in the Nebraska Panhandle staying 
mainly in the upper 30s to low 40s, with SE Wyoming staying above 
freezing in the low to mid 30s, although Laramie may briefly dip 
below freezing. For perspective, the average low in Cheyenne on 
Thursday is 30 degrees, with a low of 37 degrees currently in the 
forecast. During the day on Thursday, the mid-level ridge will begin 
to amplify over the Upper-Midwest, placing us in a SW flog regime. 
This will continue the trend of dry and warmer than average 
conditions as NAEFS guidance has 500 mb geopotential height values 
ranging from the 75-80th percentile underneath the building ridge. 
This will translate to high temperatures mainly in the low to mid-
60s east of the Laramie Range, and slightly cooler mid to upper 50s 
in places like Laramie and Rawlins. Another mild night is expected 
Thursday into Friday, with many locations in the Nebraska Panhandle 
struggling to dip below 40 degrees by Friday morning, and the 
population centers (at least for Wyoming standards) across SE 
Wyoming staying above freezing in the mid to upper 30s.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Issued at 150 AM MDT Wed Oct 28 2026

A broad, upper-level ridge will sit across the central CONUS Friday 
morning leading to modest southwesterly flow across the region. 
Unlike previous patterns, this ridge will not be as strong and 
temperatures will not warm nearly as much. The next upper-level 
system will be slowly moving into the Pacific Northwest throughout 
much of the day Friday, though its progression will be slow. The 
base of the trough will remain offshore through at least early 
Saturday morning. A very weak shortwave will attempt to push through 
the region on Friday, leading to very weak, synoptic ascent mainly 
across western Nebraska and mainly later in the day as the shortwave 
approaches the region. 700mb slow remains from the southwest and 
fairly weak, with the shortwave barely visible as it progresses 
northeastward and is, ultimately, absorbed into the larger scale 
flow. 700mb temperatures remain in the 4 to 6C range across the 
region throughout the day Friday, so expect temperatures in the 
upper-50s to low-60s everywhere. Surface is currently forecast to be 
out of the south-southeast for all locations east of the Laramie 
Range and out of the southwest for all locations west of the Laramie 
Range. By 18Z Friday the NAEFS Mean Precipitable Water will increase 
to above the 90th percentile for portions of western Nebraska and 
barely into southeast Wyoming before increasing to above the 90th 
percentile nearly everywhere east of the Laramie Range by 00Z 
Saturday. Therefore, moisture will not be a limiting factor as the 
weak forcing moves through, as has been the case for the last 
several systems. The biggest concern will be whether or not the 
ascent from the weak shortwave and systems moving out of the 
southwestern CONUS will be enough to get showers going across 
western Nebraska. If it is, these showers are expected to remain 
rain with snow not anticipated at this time.

Precipitable water values will remain well over the 90th percentile 
for most places throughout the weekend, which may put a small damper 
on Halloween festivities on Saturday evening and night. This 
disturbances off to the southwest will push towards the region on 
Saturday, increasing forcing across the region. The upper-level 
trough over the Pacific Northwest will maintain its slow movement 
inland Saturday, with the trough axis sitting over Idaho and the 
Nevada/Utah border by early Sunday morning. A few lobes of 500mb 
vorticity will eject across the CWA throughout the day Saturday, but 
these look to be weaker than what is expected for Sunday. 700mb flow 
begins to amplify later Saturday into the early morning hours Sunday 
as the 700mb system starts to take shape across western Montana. As 
of now, a strong 700mb jet looks to develop just to the northeast of 
the CWA throughout the evening on Saturday, which would likely 
increase precipitation chances west of the Laramie Range as this 
region remains in the right entrance region of the low-level jet. 
Winds will also likely start picking up Saturday night into early 
Sunday morning for this same region. Luckily, or not if you like 
snow, 700mb temperatures are expected to remain well above the -2 to 
0C range, likely in the 2 to 5C range, which favors any 
precipitation falling as rain and not snow. So what does this mean 
for trick-or-treating and other Halloween activities? Well, as of 
now, precipitation looks to hold off for the most part until early 
Sunday morning, unless you are trick-or-treating in the Snowy Range. 
Temperatures will quickly drop into the 40s for most places by 8PM 
Saturday night, so it looks like there will be a lot of superheroes, 
witches, and vampires with jackets. Luckily, precipitation should 
hold off until festivities end.

Much of the remainder of the long term forecast remains very 
uncertain as model confidence and agreement worsens Sunday through 
Tuesday. The early forecasting shift talked about the possibilities 
in depth, so please read the following for a discussion on the 
Sunday through Tuesday time period...

Forecast confidence decreases considerably as we head into the 
Sunday through Tuesday time period. While there is still potential 
for widespread precipitation, the ensemble spread is enormous as a 
very complex weather pattern sets up over the Western CONUS. First, 
a powerful disturbance will race into the southwest, riding on a 
very strong sub-tropical jet stream. Meanwhile, a northern branch 
trough will dive into the northwest and progress eastward 
simultaneously. The northern upper level low may also close off from 
the polar jet itself, adding to the uncertainty. With so many moving 
parts on the board, it is difficult to have much forecast confidence 
in how this will play out. 

In lieu of that, we can discuss some possible scenarios. 
Approximately 45% of LREF members are clustered into a scenario 
showing a more progressive storm system. This is further split 
between about half of this camp showing a storm that remains 
progressive, and half showing a storm that eventually closes off and 
strengthens, but this occurs too far east to deliver much 
precipitation to our area. In this scenario, most of the area could 
expect light precipitation amounts, generally 0.25" or less. The 
remaining 55% of ensemble members have a deeper, stronger system 
with better forcing for lift, and thus improving chances for 
precipitation. About 30% of the full ensemble suite (a subset of the 
55%) have a moderate precipitation event, where the system is strong 
and deep, but still progressive. The final 25% (again a subset of 
the 55%) depict a slow, strong upper level low closing off before 
reaching our area, which would lead to widespread heavy 
precipitation for much of the area, but especially over the High 
Plains. The ECMWF Extreme Forecast Index provides some additional 
context. EFI values for QPF on Monday are only around 0.5 to 0.7, 
suggesting low confidence in a significant event. However, the shift 
of tails values exceed 2.0 over much of the High Plains, which tells 
us that a small subset of ensemble members depict an extreme event.
Thus, the main takeaway at this time should be that at least some 
light precipitation is narrowly favored (60% chance) over much of 
the area Sunday PM into Tuesday AM, and there is potential for 
significant rain and/or snow, but the probability of this scenario 
is fairly low (25% chance) at this time. Nonetheless, this is high 
enough to discuss and continue to monitor closely in the coming 
days. Most model guidance shows limited cold air with this system 
once again, and the wettest ensemble members also tend to be the 
warmest (as these close the low off faster). This will make snow 
levels an issue once again. Regardless of the precipitation outcome, 
expect cooler temperatures by Monday with blustery conditions. There 
is potential for high winds as well, but we'll wait to get a better 
idea of the storm's evolution before diving into those details.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 509 AM MDT Wed Oct 28 2026

Low clouds and fog are ongoing at KBFF, KAIA, and KSNY this morning 
with all sites at either LIFR or VLIFR. These conditions are 
anticipated to continue through 15Z, with clouds starting to slowly 
clear as early as 14Z. All terminals are expected to return to VFR 
conditions after 15Z and throughout the remainder of the 12Z TAF 
period. Gusty winds are expected today, with a northerly wind shift 
anticipated at KCYS, KBFF, KCDR, KSNY, and KAIA later this afternoon 
into the evening hours. Low-level wind shear is possible at KCYS and 
KLAR through 16Z this morning.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...Dense Fog Advisory until 8 AM MDT this morning for NEZ003-019-
     021-055.

&&

$$

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