textproduct: Cheyenne

KEY MESSAGES

- Scattered showers and isolated thunderstorms will continue through Tuesday night. Brief locally heavy rainfall is possible.

- A more organized rain producer may graze the southern Nebraska panhandle on Wednesday, but confidence remains low in the exact track of the storm system.

- A cooler temperatures continue through Thursday, but warmer and drier weather will prevail Friday through early next week.

SHORT TERM /THROUGH WEDNESDAY NIGHT/

Issued at 242 AM MDT Tue Sep 29 2026

Upper-level troughing will continue to dominate the region throughout much of the upcoming week as multiple systems push across the CONUS. Today, the upper-level trough will finally pinch off a closed low across the southwestern CONUS by the afternoon hours, leading to a very strong jet from the Pacific Ocean northeastward through portions of the Midwest. Southwesterly flow aloft will slowly move around to due southerly by early Wednesday morning as the low continues to circulate across the Four Corners region. A large swath of 500mb vorticity will develop across the Intermountain West during the day today with the turbulent upper-levels. This vorticity swath promotes modest 500mb cyclonic vorticity advection across all of the CWA from northwest to southeast this afternoon, leading to modest synoptic forcing. Despite the turbulent upper- levels, 700mb winds will be weaker throughout the day, switching from southwest to northeast by early Wednesday morning. The 700mb shortwave will weaker as the upper-level trough pinches off the closed low, favoring the relatively quite 700mb flow. Weak to modest 700mb warm air advection is expected as temperatures warm from the 3 to 5C range this morning into the 6 to 8C this afternoon. Overall, precipitation chances will be lower this afternoon compared to previous days due to the erratic atmosphere. The best chances for precipitation will be confined to the southern portions of the CWA with PoPs around 15 to 25 percent, decreasing into the evening hours as low-level winds flip around to the north and the best forcing moves out of the region. Temperatures will remain cool again today with overcast skies expected again. Surface temperatures will only warm into the low-60s to mid-70s this afternoon, with the mountain remaining around 40 to 50F. The overcast skies will also prevent any significant destabilization of the atmosphere this afternoon and will keep any thunderstorms at bay.

The turbulent atmosphere will continue for Wednesday as the closed low over the Four Corners regions starts to absorb Hurricane Polo as it ejects eastward into the Southern Plains. As the upper-level low pushes eastward, much of the CWA will be under little to no significant steering flow at 250mb as it remains in the quiet region due north of the progressing low. This low is currently anticipated to continue its eastward progression and become more narrow (west to east). As a result, the 500mb vorticity maxima look to just to the southeast of the CWA, potentially just passing overhead in Cheyenne County Wednesday afternoon. As the low starts to eject northward early Thursday morning, it is currently progged to remain just off the southeast of the CWA. The 700mb flow will be a touch more exciting early Wednesday morning throughout the early afternoon hours as two 700mb lows attempt to develop before the northeastern low of western Kansas becomes to dominant low and absorbs the other. The dominant low will intensify quickly Wednesday afternoon, but struggles to eject very far to the northeast. This low will still be over western Kansas by Wednesday evening into the overnight hours. Easterly to northeasterly 700mb flow is expected across the CWA, favoring the potential for upslope development along and east of the Laramie Range. 700mb temperatures will remain quite warm in the 5 to 7C range through the afternoon hours before cooling into the 3 to 5C range across southeastern portions of the CWA as the 700mb low advances. If 700mb temperatures were a few degrees cooler, below 0C, this could be quite the winter event with precipitable water above the 90th percentile thanks to additional tropical moisture. However, warm temperatures win and precipitation is expected to only be rain and thunderstorms. The bigger question will be how far north and west the precipitation makes it. As of now, the currently projected path of this system would keep the precipitation confined to a line from Cheyenne to Alliance and points southeast. If the track were to shift more northwestward, precipitation chances would extend northwest past the Cheyenne to Alliance line. Despite this, breezy north to northeast winds are expected Wednesday as the surface low increases pressure gradients across the region along with increased 700mb height gradients. Cloudy skies will persist Wednesday before slowly clearing as Thursday morning approaches.

LONG TERM /THURSDAY THROUGH MONDAY/

Issued at 242 AM MDT Tue Sep 29 2026

Much quieter weather returns for the second half of the week as 250mb flow turns northwesterly to westerly behind the departing trough. Northwesterly flow on Thursday will keep temperatures cool across the CWA with highs currently forecast to be in the 60s everywhere. Little to not precipitation is anticipated on Thursday as subsident flow remains in place. A warming trend will start Friday and continue through the weekend as a ridge attempts to build across the western CONUS. Temperatures will warm into the upper-60s to mid-70s with no precipitation expected as the moisture plume from the Pacific Ocean remains cutoff. Upper-level ridging will continue to build into the weekend as a trough digs southward just off the coast of California. This system could be the next precipitation producing to impact the region, but for the remainder of the long term forecast period it remains well off to the west. Temperatures on Saturday will warm into the upper-60s to mid-70s with temperatures on Sunday following suit, in the upper-60s to mid-70s. Temperatures start to warm more Monday onwards as an upper-level ridge builds ahead of the incoming trough off the coast of California. Highs on Monday are currently forecast to be in the mid- 70s to low-80s, with slightly warmer temperatures possible on Tuesday, depending on the system's track.

The system off the coast of California could start to impact the region as early as Monday morning, with long range models currently suggesting a brisk eastward movement through the weekend. The GFS and ECMWF are in fairly good agreement on this system with the 00Z runs, though the GFS positions the trough slightly further north than the ECMWF. Models disagreement starts to increase into Tuesday morning, with the GFS suggesting a more progressive trough while the ECMWF slows the trough down and keeps it much further west. Long range models suggest precipitation chances starting to return to start the work week, with low-end PoPs over western portions of the CWA as soon as Monday afternoon.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1100 PM MDT Mon Sep 28 2026

VFR conditions will prevail across the terminals for the duration of this TAF period. A few exceptions are KSNY and KAIA where BR may form and obscure VIS down to 4SM. Otherwise no other aviation concerns for the overnight hours as winds will remain light and variable. Additional moisture will push in from the south, increasing chances of precipitation for KCYS, KAIA, and KSNY. At this time, confidence is low on the placement and timing, so kept any mention out of the TAFs for this forecast period.

CYS WATCHES/WARNINGS/ADVISORIES

WY...None. NE...None.