textproduct: Cheyenne

KEY MESSAGES

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

- A brief drying trend expected for the weekend, ahead of a potential strong Pacific storm system moving into the Front Range early next week.

SHORT TERM /THROUGH FRIDAY NIGHT/

Issued at 210 AM MDT Thu Sep 24 2026

Pretty quiet early this morning as yesterday evening's thunderstorm activity has pushed well east of the forecast area. Early morning temperatures are pretty mild due to the cloudy skies across the region and south to southwest flow aloft bringing in additional subtropical moisture. Did add some patchy fog where some clearing is taking place, mainly over the northern and central Nebraska panhandle with SREF and HREF probability of fog (VIS below 4 miles) around 20 to 40 percent. Otherwise, no other changes made to the forecast through noon Thursday.

Models have continued to back off on rainfall and thunderstorm chances for later Thursday and Thursday night. For much of today, model soundings show stable low to midlevels with poor lapse rates and hardly any instability until this evening...as some cooler air aloft moves overhead. High res CAMS agree with this solution and don't show much activity until late this afternoon and into he evening hours. Kept most of the area dry with POP below 10 percent until this evening. All models in better agreement showing the upper level disturbance, which is responsible for the heavy rainfall across New Mexico and western Texas, lifting northeast and ejecting east across the forecast area. The best dynamics will be south and east of the northern Front Range. The trough axis will also lift across the area late Thursday night and Friday morning, with limited instability and forcing. Lowered POP across the whole forecast area. Still expect some scattered showers and isolated thunderstorm, but this activity looks to confine itself to the I-80 corridor and not even as far north as the North Platte River. However, any heavy rain showers are not expected to move much tonight, so can't rule out a minimal excessive rain threat along the I-80 corridor especially with PWATs near the 95th to 99th percentile for this time of the year. Increased max temperatures a few degrees due to the lack of precipitation for most of the day.

All models show some drier air moving into central Wyoming as low to midlevel winds shift into the west. However, models show the upper level disturbance taking its time ejecting east. Increased POP in the mountains and for areas along and east of the Laramie Range Friday afternoon and evening for widely scattered thunderstorms and periods of showers. All models show better instability as well with the trough axis overhead and dewpoints remaining in upper 40s to mid 50s ahead of the dry air intrusion. Afternoon temperatures expected to be near seasonal averages and generally in the upper 60s to upper 70s (warmest below elevations of 4500 feet).

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Issued at 150 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 /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 550 AM MDT Thu Sep 24 2026

A subtropical upper level disturbance will slowly lift northward across the Rocky Mountain region through Friday before ejecting eastward. Mostly cloudy skies will continue with isolated showers and thunderstorms. Areas of fog expected late tonight as this disturbance lifts northward into the area.

HAZARDS/WEATHER TRENDS: VFR conditions will prevail through 06z Friday. Some lingering early morning low CIGS possible near KAIA, KSNY, and KBFF, but coverage is low enough to keep out of the TAF. A few thunderstorms may form this afternoon and this evening, but coverage will be very limited to along and south of the Interstate 80 corridor. High confidence that low stratus and fog will develop across the high plains late tonight after 06z Friday, impacting KAIA, KSNY, and possibly KBFF and KCYS towards 12z Friday.

CYS WATCHES/WARNINGS/ADVISORIES

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