textproduct: Cheyenne

KEY MESSAGES

- A plume of monsoon moisture will arrive on Monday, moderating temperatures and improving rainfall chances through Wednesday.

- Marginal to Slight Risk of Severe Thunderstorms Monday through Wednesday. Strong gusty winds will be the primary threat.

- Heavy rainfall and localized Flash Flooding possible Tuesday through Wednesday night.

SHORT TERM /THROUGH WEDNESDAY/

Issued at 1251 AM MDT Mon Jul 27 2026

Current KCYS radar loop shows a few bands of showers and embedded thunder lingering across the western Nebraska panhandle at 200 am, with some more isolated activity located near the mountains of southeast Wyoming. This set up will likely continue over the next several days with a decent monsoon push underway over Wyoming, Colorado, and Nebraska. Low to midlevel moisture advection will continue into Monday with PWATs increasing to 1.00 (west) to as high as 1.60 inches (east). This moisture will likely remain over the area through Wednesday with all models in good agreement, showing PWATs as high as 1.75 inches for the eastern plains. NAEFS remains between the 90th to 98th percentile for PWAT compared to climatological norms for late July, which is pretty impressive considering late July/early August typically experiences monsoon rainfall. Showers and thunderstorms are expected each day through Wednesday afternoon, and some of this activity could linger into the overnight hours like we are experiencing early this morning.

With the arrival of higher moisture, slightly cooler temperatures are expected over the next few days. We will likely have a brief pause in the 100 degree temperatures with high and low temperatures closer to average for this time of the year (low/mid 80s along and west of I-25/upper 80s and low 90s east of the I-25 corridor). However, considerable cloud cover might keep low temperatures slightly elevated. Tuesday should be the "coolest" day with highs in the mid 80s to low 90s across most of the area, coolest along the I-80 corridor where the best chance for showers and thunderstorms will likely be.

As for thunderstorms, SPC has upgraded the Marginal risk for severe thunderstorms to a Slight Risk for about half of the western Nebraska panhandle for Monday afternoon and evening. Primary threat will be strong gusty winds over 70 MPH with a small large hail threat since inverted-V soundings will still be present for much of the day, but gradually moistening of the boundary layer should occur late in the afternoon and through the evening hours. Not much shear today with mainly straight hodographs, especially later in the day, which favors straight line winds. A few of these lines of storms may become organized enough to produce some marginally large hail, but believe that will be very isolated. Also, upper level short wave feature appears to move relatively quick today, exiting the region as early as mid to late afternoon. So not very confident about long duration lines of thunderstorms at this time, but isolated weak cells may still produce isolated areas of very strong wind gusts in this set up. For Tuesday and Wednesday, a branch of the 70kt upper level jet to our north will sneak into the forecast area, this feature will likely provide increasing upper level forcing, but more importantly, increasing midlevel shear. Models also show the next shortwave feature moving east much slower around the periphery of the upper level high. This vort max could be pretty potent as it tracks southeast across the area, so would not be surprised if thunderstorm activity linger past midnight Tuesday night/early Wednesday morning. Similar conditions are expected on Wednesday with a better defined potent Pacific upper level trough (for this time of the year anyway) tracking across the Front Range. Flash Flooding will also become more of a concern on Tuesday and Wednesday due to training/slow propagation of storms and PWAT approaching 1.75 inches. Large hail looks slightly more favorable by midweek, but the 0c to -20c layer still looks rather elevated and sub-optimal.

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

Issued at 323 PM MDT Sun Jul 26 2026

Higher probabilities of afternoon showers and thunderstorms will characterize the first portion of the long-term forecast period as an enhanced push of monsoonal moisture moves through southeast Wyoming and western Nebraska. Both ECMWF ensemble and GEFS ensemble guidance show PWAT normalized anomalies peaking near the 2 standard- deviations threshold through Wednesday afternoon. PWAT values between 1 inch and 1.25 inches are seen in forecast soundings during the afternoon hours. Additionally, a bit of enhanced westerly flow aloft in the 500-200mb layer will round the apex of the monsoonal ridge over the southwestern CONUS. This enhanced flow aloft, while certainly not extreme, will be just enough to add a bit higher bulk shear values to the convective setup. Convection will likely develop over the higher terrain of southeast Wyoming and drift east-southeastward by 18-20z. As outflow boundaries pool, expect a chance of isolated gusty winds perhaps occasionally to severe limits of 50 knots in the eastern high plains of Wyoming and western Nebraska. While temperatures will run slightly cooler the enhanced monsoonal moisture, deeply mixed afternoon forecast soundings continue to support a gusty wind threat. Thunderstorms should have enough forward momentum to limit the risk of flash flooding. However, any location that does see repeated rounds of showers and thunderstorms could experience brief flash flooding concerns.

By Thursday, the monsoon high pressure over the southwest becomes a bit more suppressed and the plume of higher moisture values drifts eastward away from the Rocky Mountain region. As a result, expect lower chances of afternoon showers and storms from Thursday through next weekend. High temperatures will rebound somewhat as we dry out, but some uncertainty in the temperature and precipitation forecast emerges by the weekend. A frontal boundary from the northern high plains attempts to drop southward into the eastern plains of Wyoming and western Nebraska perhaps as early as Friday afternoon. Ensemble guidance varies greatly with regard to any impacts...ranging from only slightly cooler temperatures to a frontogenetically forced band of showers and cloud cover over the high plains on Friday evening, or perhaps on Saturday. With such low confidence from Day 5 onward in the forecast, we will message a more conservative outcome for now with slightly less hot weather and isolated shower chances. Regardless, significant precipitation seems unlikely through the end of the long term with generally above-average temperatures continuing for the foreseeable future despite a few frontal boundaries nearby.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 550 AM MDT Mon Jul 27 2026

Plume of monsoon moisture will enter the area today with slightly cooler temperatures and a better chance for showers and thunderstorms this afternoon and this evening. Primary concerns will be strong gusty winds and brief heavy rainfall between 19z today and 02z Tuesday.

HAZARDS/WEATHER TRENDS: VFR conditions will prevail over the next 24 hours. Brief MVFR VIS possible with any shower and thunderstorm activity that develops over the mountains and pushes eastward into the high plains after 20z. Timing is uncertain, so added PROB30 groups for TS activity for most terminals.

CYS WATCHES/WARNINGS/ADVISORIES

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