textproduct: Cheyenne

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 /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 1049 PM MDT Tue Oct 27 2026

Main aviation impact tonight will be low stratus and fog developing in the Nebraska panhandle. Light southerly winds will increase low- level moisture leading to the fog and low stratus. Visibility reductions and CIG categories are expected to be IFR at KSNY, KAIA and KBFF later tonight and into Wednesday morning. Clouds will lift and fog is likely to burn off by mid-morning. Clouds will clear out by the afternoon, leading to a mostly sunny but breezy day across the area.

CYS WATCHES/WARNINGS/ADVISORIES

WY...None. NE...Dense Fog Advisory until 8 AM MDT this morning for NEZ003-021- 055.