textproduct: Cheyenne

KEY MESSAGES

- A stormier weather pattern will setup Tuesday and Wednesday and continue into the weekend with daily chances for PM showers and thunderstorms.

- Increasing potential for strong to severe thunderstorms is being monitored late in the week and during the weekend.

SHORT TERM /THROUGH WEDNESDAY NIGHT/

Issued at 230 AM MDT Tue May 26 2026

Not many changes made to the previous forecast package for the middle of the week. Quiet weather early this morning as the last few rain showers are dissipating over the eastern plains. Remaining at least partly cloudy through sunrise, which should keep low temperatures mostly in the 50s, with mid to upper 40s along and west of I-25. For today, models continue to show a broad upper level trough/disturbance lifting northeast out of Arizona and across the four corners region by midday today. A strong Pacific storm system will continue to dig south and parallel the Oregon coastline earlier today before it redevelops across the western Great Basin region late tonight. The disturbance across Arizona is therefore expected to accelerate northward ahead of the main upper level low to the west, with increasing coverage of showers and thunderstorms today. However, this activity should be mainly confined along and west of the I-25 corridor for much of the day since the main vort axis and upper level jet dynamics will mainly be located across Carbon and Albany counties through much of the day. Further east, some outflow boundary initiation and/or terrain influence is possible for convection initiation, but the best coverage should be west of the Laramie Range. High res models continue to show heavy rain showers and scattered thunderstorms lifting north across southeast Wyoming between noon and midnight tonight. Multiple bands are expected with NAEFS continuing to show PWAT over the 90 to 95 percentile (today and Wednesday). As for strong to severe weather, it appears highly unlikely at this time due to MLCAPE below 400 j/kg and quick initiation and multiple bands through the day. There is some threat of strong gusty winds though, with high res guidance showing some decent outflow near the first several bands this afternoon. Will need to monitor any heavy rainfall in the mountains with recent heavy snow pack (2 to 3 feet in some areas) observed with the last storm system for rapid runoff/local flooding concerns (low confidence/low areal coverage). Remaining warm today, but noticeably cooler west of the Laramie Range with highs in the upper 60s to low 70s.

For Wednesday, models show the best chance for showers and thunderstorms shifting east into far eastern Wyoming. There is a little uncertainty starting to creep into the forecast for Wednesday, with models now showing the disturbance over Texas retrograding westward a bit into Colorado and drifting northward through Wednesday night. This is in response to the expected Rex block taking shape over the central plains. Increased POP through the late evening hours towards Thursday morning. Again, convective parameters are subpar for severe weather since we'll have little 0-6km shear over the region and limited CAPE. Moisture shouldn't be a problem with dewpoints climbing into the low 50s and PWAT climbing over the 97th percentile for this time of the year. There is some upper level forcing, so kept POP above 50 percent for most of southeast Wyoming and southwest Nebraska. It will be a few degrees cooler compared to Tuesday with highs in the upper 60s to mid 70s for most of the forecast area, and in the low to mid 80s across east central Wyoming and the northern Nebraska Panhandle.

LONG TERM /THURSDAY THROUGH MONDAY/

Issued at 1250 PM MDT Mon May 25 2026

For mid to late week, eastern Wyo and western Neb sit between the large closed low anchored near the Great Basin and the amplified ridge over the Great Plains. Low level and upper flow will primarily be south/southeasterly through the extended period for the forecast area. This pattern will maintain near to slightly above normal temperatures (highs in the 70s and 80s) and periodic precipitation chances. While the near surface flow will not be uninhibited from the Gulf, dew points will remain around 50F east of I-25 through the workweek, which can be sufficient for thunderstorm activity. The core of the upper dynamics remain west of the immediate region, but large scale ascent should extend downstream from the main low and influence the southern Wyo ranges and adjacent areas. Perhaps the greatest potential for widespread moisture comes Wednesday as a mid- level shortwave traverses the High Plains. Thunderstorm activity should increase through the afternoon, taking advantage of elevated instability/lift and a ribbon of moisture. Thunder parameters don't appear to support severe weather at this time, as overall CAPE is limited and deep layer shear is weak. Friday could be a different story, however. The upper jet swings a bit to the east, placing the panhandle in the sweet spot for increased lift. A surface low also emerges from the northern Rockies, along with a notable change in low level moisture flux over the Plains. Early indications reveal very steep lapse rates (~9C/km) and sufficient CAPE (1000+ MU j/kg) over the panhandle. Will need to continue to monitor later forecast trends regarding severe potential during the afternoon and evening. Some mechanisms remain in place over the weekend, so will hold status quo for chance PoP and seasonable temps.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 600 AM MDT Tue May 26 2026

An upper level disturbance will accelerate as it moves northward today into central Colorado and Wyoming. This disturbance will bring numerous showers and scattered thunderstorms to mainly southeast Wyoming today and into tonight. Gusty south to southeast winds are expected for most terminals between 15z this morning and 04z Wednesday.

HAZARDS/WEATHER TRENDS: Gusty winds out of the south will begin over the next few hours with gusts up to 40 knots likely for all terminals after 18z, with the exception of KRWL. Showers and thunderstorms will develop across the mountains and move northward into KLAR and KRWL after 18z. KCYS may see some of this activity later in the afternoon and evening hours. MVFR CIGS and VIS possible with these thunderstorms along with erratic gusty winds.

CYS WATCHES/WARNINGS/ADVISORIES

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