textproduct: Cheyenne

KEY MESSAGES

- Drier, warmer, and breezy to windy conditions are expected to continue through Wednesday. Another round of morning fog is possible over portions of the High Plains Wednesday AM.

- 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 148 PM MDT Tue Oct 27 2026

It's still a bit breezy this afternoon as the 700mb jet slowly begins to calm down. While high winds aren't expected this afternoon wind gusts between 45 and 55 mph can still be anticipated on I-80 between Rawlins and Laramie as well as I-25 in between Casper and Douglas. As the system continues to lift back into the Canadian Providences we will continue to see the 700mb jet weaken and the upper level ridge begin to take back over. Other than some high level clouds moving through the area not much should be expected in the short term forecast. Another weak shortwave is expected to be passing through the Intermountain west tonight. We will see some increased cloud cover and stable temperatures overnight around 40 to 45 degrees. But otherwise any precip chances look to be contained in the Northwestern portion of Wyoming and possibly Central Wyoming. Under this ridge 700mb temperatures are going to be around 6C which means high temperatures will be around 60 to 65 for locations east of the I-25 corridor and between 50 and 55 for the higher elevations west of the I-25 corridor.

LONG TERM /FRIDAY THROUGH TUESDAY/

Issued at 255 PM MDT Tue Oct 27 2026

On Friday, we will once again see a broad ridge in place over the Central CONUS. This iteration of this familiar weather pattern will be less amplified, not supporting warmth as significant as what we had earlier this month. With troughing inching into the west coast, southwest flow aloft will continue to prevail. Models are in fairly good agreement showing low-level south to southeast winds advecting in improved low-level moisture to the High Plains Friday while moisture aloft improves with another influx of tropical moisture. By the end of the day Friday, NAEFS mean precipitable water exceeds the 90th percentile of climatology for much of the area. As has been our problem frequently as of late, we will not have much forcing for ascent, despite the abundant moisture. This begins to change Friday night as two disturbances are pulled out of the southwest. The first will be associated with the remnant moisture of Tropical Storm Vance, the latest in the parade of eastern Pacific tropical systems pushed into the southwest CONUS. This remnant vort-max will track further east than its predecessors, moving mostly over the Plains. There is a possibility (about 30% chance) for some showers Friday night into Saturday, mainly in the Nebraska panhandle. Another more disorganized vort-max tracking further west will bring potential for afternoon and evening showers and high elevation snow showers mainly to the mountains and adjacent zones on Saturday (Halloween). Other than the potential for a few light showers, expect generally good trick-or-treat conditions with highs in the mid 50s to mid 60s and overnight lows dropping only into the upper 30s to mid 40s. Winds look fairly light as well.

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 543 PM MDT Tue Oct 27 2026

Main aviation impact overnight 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...None.