textproduct: Cheyenne

KEY MESSAGES

- Cool but seasonable temperatures will continue through mid- week, with a warming trend expected for the weekend.

- Increasing coverage of showers and thunderstorms expected through Thursday as a subtropical disturbance lifts northward over the area, then a brief drying trend for the weekend.

SHORT TERM /THROUGH FRIDAY/

Issued at 148 PM MDT Wed Sep 23 2026

Tonight...Almost a carbon copy of yesterday, with respect to the moist low level airmass, as detected in surface analysis and with an 850/700 mb theta-e ridge axis extending north to south across far southeast Wyoming with a low level convergence axis from Cheyenne to Lusk. Much as depicted in the HRRR runs, which have been consistent, leading to more believability, isolated to scattered showers and some thunderstorms expected this evening south of a line from Laramie to Alliance. Boundary layer saturation and pattern similarity leads to moderate to high confidence in areas of fog, dense at times, after midnight over the Nebraska Panhandle and far eastern Wyoming.

Thursday...Once again, a moist low and mid level airmass exists under weak flow aloft, with a low and mid level theta-e ridge axis near the Colorado state line, thus with moist upslope east winds, we anticipate scattered afternoon and evening showers, and isolated thunderstorms south of a Rawlins to Chadron line.

Friday...Scattered showers and some thunderstorms will continue early in the morning hours with a weak shortwave trough aloft over the region. A somewhat drier airmass will advect across our counties, effectively limiting shower and thunderstorm coverage, though still cannot rule out widely scattered showers and thunderstorms near the Colorado state line, and north of a Lusk to Alliance line.

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/

Issued at 148 PM MDT Wed Sep 23 2026

We begin the weekend on a warm and dry note as the primary surge of monsoonal moisture lifts off to the north and east in conjunction with the ejecting shortwave trough that has the chance to bring us some beneficial moisture the day prior. This will result in well above-average temperatures during the day, with forecast highs anticipated to be 5-10 degrees warmer than climatology. For reference, the average high for Cheyenne on September 26 is 68F (yes, we are down into the 60s for averages now!) and 75F for Scottsbluff. With the absence of any forcing throughout the day thanks to the building ridge and 500 mb height rises, expect dry conditions. Fire concerns are minimal at this time as 25th percentile afternoon RH values are only expected to range from 15- 20%, however median peak gusts will be in the 20-25 mph range across SE Wyoming. Further, fair overnight recoveries of 50-60% are expected, keeping us below elevated fire weather criteria.

A similar pattern will remain in place on Sunday with above-average temperatures and mostly dry conditions expected. Still, little to no concern for fire weather as minimum RH values will stay well-above 20%. Long-range ensemble guidance is hinting at another influx of monsoonal moisture being advected via SW flow on the western periphery of the ridge, with PWAT values ranging from the 90th-95th percentile relative to climatology. Deterministic runs show little in the way of any synoptic-scale forcing for ascent to actually utilize this anomalous moisture and translate it to precipitation at the surface at this time, unfortunately.

Monday looks to be a bit more active than over the weekend as we maintain the supply of monsoonal moisture out of the southwest. NAEFS guidance has PWAT ranging from 2-4 sigma at this time, with our region situated ahead a somewhat amplified positively-tilted shortwave trough over the Great Basin. This should provide at least some forcing for showers and thunderstorms heading during the day. The threat for any heavy rain is uncertain at this time as the forcing isn't anticipated to be all that widespread, and although PWAT will be on the high end of the distribution, we are getting to that time of year where widespread and prolonged forcing gives us our most beneficial moisture, rather than a single thunderstorm with extreme rainfall rates that manages to sit over a localized area. Unsurprisingly due to more moisture and therefore clouds/potential precipitation, highs on Monday will be a bit cooler, though still a few degrees above average. Although exact timing is highly uncertain at this range, a cold front looks to push across SE WY and the Nebraska Panhandle sometime during the day on Monday, which will decrease our temperatures as we head into the middle of next week.

The shortwave trough skirts across the area on Tuesday, placing us in more of a WNW flow regime. This will shunt off our supply of subtropical moisture leaving us with drier conditions, especially in the cooler, post-frontal air mass. Maybe our first actual taste of fall that is long overdue? We shall see...

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1135 AM MDT Wed Sep 23 2026

Fog and low clouds are in the process of mixing out across the Nebraksa Panhandle this morning, and this trend is expected to continue into the afternoon, with primarily VFR prevailing. KBFF and KSNY are currently under MVFR CIGs, however cloud bases are expected to increase to VFR criteria within the next few hours. Kept a PROB30 group for -TSRA at KCYS this afternoon where confidence is highest that showers and thunderstorms will directly impact the terminal, however much lower confidence that KLAR, KBFF, and KSNY will be impacted. Thus, have opted for VCSH for these areas where coverage is expected to be lower. While not as prevalent as the previous couple of days, can expect more low cloud/shower development starting overnight and carrying into the morning hours, primarily for the NE terminals, where MVFR CIGs are anticipated in the vicinity of any showers.

CYS WATCHES/WARNINGS/ADVISORIES

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