textproduct: Cheyenne

KEY MESSAGES

- Areas of fog will develop after midnight tonight and continue through Wednesday morning south of a line from Laramie, to Torrington to Alliance with some dense fog possible near the Interstate 80 Summit and the southern Laramie Range Foothills.

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

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

SHORT TERM /THROUGH THURSDAY NIGHT/

Issued at 211 PM MDT Tue Sep 29 2026

Tonight...The closed upper low aloft moves from southeast Arizona to the Arizona-New Mexico state line by dawn. Primary challenges during this period will be the northern extent of the precipitation shield associated with the low aloft, and the moisture incorporated into the system from the tropical system Polo, as well as fog and dense fog possibilities from rather deep upslope from the southern Laramie Range eastward to Cheyenne and the southern Nebraska Panhandle.

Prefer the NAM handling of the mesoscale and synoptic pattern due to trends and its rather high resolution. Expecting areas of fog to develop after midnight from the I-80 Summit and southern Laramie Range eastward across Cheyenne and Laramie County and to the southern Nebraska Panhandle. Considering boundary layer progs with wind direction and relative humidity, it looks like areas of dense fog may develop across the southern Laramie Range and I-80 Summit and the eastern Laramie Range foothills after midnight. With widespread mid level cloud cover spreading northward across our southern counties, fog may be somewhat limited in expanse and duration, though felt confident enough to include areas of fog from Laramie to Cheyenne to Sidney, with areas of dense fog from the I-80 Summit and southern Laramie Range to along or just west of Cheyenne including the southern Laramie Range foothills. We may see some drizzle or very light rain spread across our far southern counties near the Colorado state line after midnight.

Wednesday...The wobbling upper low moves to southeast Colorado and northeast New Mexico by suppertime. The NAM looks best with its' depiction of the precipitation shield and thus have continued to paint scattered showers south of a line from Laramie to Sidney, although the best areal coverage will be near the Colorado state line, where lift will be maximized due to 500-300 mb and 700-500 mb quasigeostrophic forcing combined with the decent precipitable water values and atmospheric moisture depth and mechanical upslope lift. It looks like areas of fog will continue until noon for locations near the Colorado state line and near the I-80 Summit. The northern extent of the precipitation shield will be limited by rather dry low levels and negative theta-e advection undercutting the moist mid levels.

Wednesday night...Our closed low aloft moves slowly to the Colorado- Kansas state line by sunrise with the northern shield of the precipitation concentrated over northeast Colorado and will continue to blend in with our neighboring offices grids for POPS at North Platte and Denver/Boulder. The sharp discontinuity in the precipitation shield will need to be watched closely.

Thursday/Thursday night...The trough aloft opens up and moves southeastward over Kansas and Oklahoma, with west northwest flow aloft over our counties. Although we will still see some mid and high level cloud cover, no precipitation is anticipated due to minimal lift.

LONG TERM /FRIDAY THROUGH MONDAY/

Issued at 211 PM MDT Tue Sep 29 2026

Generally tranquil weather will persist through much of the long- term period. Large-scale ridging will dominate the weather pattern over the western CONUS resulting in generally mild above-average temperatures and limited precipitation chances over southeast Wyoming and western Nebraska. This ridging pattern is, broadly speaking, a general result of the highly active tropical pattern over the eastern Pacific. As the firehose of EPAC tropical storms move west and then recurve to the north in the mid-latitudes of the central Pacific, potent synoptic troughing is noted over the Bearing Sea/Gulf of Alaska which thus drives downstream ridging over western North America. These types of stable-synoptic-wave patterns can often persist for weeks or more, locking in high-confidence forecasts over much of the west including our region.

Regarding local details in the forecast, expect above-average temps from Friday onward. High confidence exists in temps around 5 degrees above average this weekend (low to mid-70s east of the mountains) and highs 10 to 15 degrees above average through next week. Despite the drier weather in place late this week and through the weekend, rising heights should result in overnight lows remaining above average as well. This should hold off any threats of frosts (or freezes) for any populated area of southeast Wyoming outside of the mountains. Afternoon RH values will drop to near or slightly below 20% throughout the weekend during the afternoon hours across all of southeast Wyoming and portions of the Nebraska panhandle. However, generally light surface flow out of the west less than 20 mph will likely preclude the need for any fire weather headlines. Overall, given the synoptic pattern described earlier in this discussion, forecast confidence is quite high throughout the entire long-term period with limited impacts expected.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1106 AM MDT Tue Sep 29 2026

VFR conditions will dominate at all terminals this afternoon. Expect generally light and variable winds less than 8kt with sky conditions generally remaining clear to mostly sunny. Expect a mostly clear overnight at all terminals with light winds continuing. On Wednesday morning, expect lower ceilings to move in at SNY after sunrise with drops into MVFR and perhaps IFR category by 18z. Isolated showers will also affect SNY as early as 16z on Wednesday.

CYS WATCHES/WARNINGS/ADVISORIES

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