textproduct: Cheyenne

KEY MESSAGES

- Shower and thunderstorms are expected later on Monday and into Monday night. Strong wind gusts and heavy rainfall possible.

- Drying and warming trend expected going into mid to late week with growing potential for elevated fire weather conditions, mainly north of Interstate 80.

SHORT TERM /THROUGH TUESDAY NIGHT/

Issued at 210 AM MDT Mon Aug 31 2026

As expected, pretty quiet weather early this morning with decreasing cloudiness over the area and temperatures responding by falling into the mid 50s just after midnight. Yesterday's convection underperformed with most of the area only seeing some light rain showers and quite a bit of wind. Expect Monday to be mostly low impact as we turn our attention to the upper level trough and next monsoon push, located across south central California and Arizona at this hour. This trough is trending even slower than yesterday's model runs, which is likely going to impact what southeast Wyoming and western Nebraska experience going into late this afternoon and into tonight.

Again, models are trending later in the day with the onset of precipitation and possible thunderstorm activity...with most synoptic models holding off until around sunset along the I-80 corridor. High resolution CAMs aren't much better, with showers and thunderstorms developing between 5 PM to 8 PM. Not only is precipitation delayed due to the slow movement of the trough, but models soundings show a very dry airmass in the midlevels and aloft. This airmass will likely mix down to the surface to some degree across central Wyoming where daytime relative humidities may bottom out near 10% to 15%. This will likely delay the precipitation even later into the evening hours and cut down on QPF amounts. For this afternoon, expect mid to high cloudiness to push north ahead of the trough later in the day, with gradual, but slow, moistening of the midlevels. There is some decent synoptic/mesoscale lift with this upper level trough as it moves northward with good mid to upper level diffluent flow, some low level convergence and CAPE values between 300 to 600 j/kg. However, the dry air aloft and slower movement has capped QPF amounts mainly below one half inch to closer to 0.10 to 0.25 of liquid at best. All ensemble means have lowered by about half of they were showing yesterday with the 90th percentile now below a third of an inch (yesterday's 00z run were close to 0.75). Understandably, WPC has pulled back on their Slight Risk for excessive rainfall as even a Marginal even seems questionable at this time given recent model trends. Therefore, kept POP about the same but expect a "High POP/Low QPF" event for most of southeast Wyoming and western Nebraska tonight through early Tuesday morning. Otherwise, temperatures will be seasonable today with highs in the upper 70s to upper 80s (warmest below 5000 feet) and a continuation of breezy conditions across southeast Wyoming.

For Tuesday, all models in good agreement showing rain shower activity ending between 900 am to noon as the trough axis lift north and exits the forecast area by the early afternoon hours. Drier air and a shortwave ridge axis will push into the area behind the trough, allowing for a relatively pleasant Tuesday with breezy westerly winds but highs returning to the mid 70s to mid 80s. There is a chance this trough slows down even further, which may keep unsettled weather and cloud cover over the eastern plains through the afternoon, resulting in lower temperatures. However, models have been consistent with the exit of this feature, so kept the current forecast as is. Coolish temperatures possible late Tuesday night with clearing skies as lows dip into the 40s and low 50s along and west of Interstate 25, with mid to upper 50s further east. Drier weather will likely extend into the middle of the week as all model soundings showing quite a bit of dry air aloft above 600mb, which will likely cap any daytime convection...even though the surface to 600mb level will remain relatively moist due to remnant surface moisture across the plains.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Issued at 1155 AM MDT Sun Aug 30 2026

The long term period will feature a warming and drying trend as mid- level heights rise over our region and the bulk of any forcing for ascent remain to the north or west of our area. Tuesday will feature a slight chance of late day showers and storms as moisture remains trapped underneath the ridge and we remain in SW flow pattern (PWAT around the 70-80th percentile), however coverage is expected to be lower relative to today and Monday. High temperatures will again remain close to climatology, with highs in the 80s east of the Laramie Range and mainly 70s out west.

We begin to heat up on Wednesday and Thursday as the ridge axis becomes focused closer to the Northern Great Plains. This will turn our attention to potential fire weather concerns as long-range ensemble guidance has signals for gusty winds and daytime RH values ranging from 15-25% especially north of the I-80 corridor. Highs will peak in the upper 70s to near 80 degrees west of the Laramie Range on both days, with much of the Nebraska Panhandle soaring into the low to mid 90s, which is still a few degrees short of record highs.

As we end the work week and head into the weekend, the ridge begins to amplify and establish itself over the Central and Southern Great Plains, resulting in a containing trend of above-average temperatures and primarily dry conditions. There are some signals of an additional push of monsoonal moisture on Saturday and Sunday, however confidence isn't high enough at this time to mention any widespread precipitation for the region.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 545 AM MDT Mon Aug 31 2026

A potent upper level trough with some subtropical monsoon moisture is forecast to lift north and move across the northern Rockies later this afternoon and tonight. Scattered showers, some thunderstorms, and lower CIGS are expected into early Tuesday morning.

HAZARDS/WEATHER TRENDS: VFR conditions will prevail today and into this evening. Rain showers and thunderstorms will develop across the Colorado mountains ahead of the upper level trough and move north into the Interstate 80 corridor, mainly impacting KLAR, KCYS, and KSNY before 09z. However, limited impacts are expected from this activity with a low probability of thunder and very low (<10%) probability for MVFR or lower conditions through tonight. Kept showers in the forecast for now with PROB30 groups for the most likely areas to see some thunderstorm activity. For the other western Nebraska terminals, impacts won't begin until after 12z Tuesday.

CYS WATCHES/WARNINGS/ADVISORIES

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