textproduct: Cheyenne

KEY MESSAGES

- Cool and seasonable temperatures will continue through mid- week, with a warming trend expected for the second half of the week into the weekend.

- Limited precipitation chances Tuesday evening into Wednesday, with a brief dry pattern starting Friday and lasting through the weekend.

- Breezy conditions will be possible across much of the region Tuesday and Wednesday, especially across the western Nebraska Panhandle.

SHORT TERM /THROUGH WEDNESDAY NIGHT/

Issued at 338 PM MDT Mon Sep 21 2026

The upper level low responsible for yesterday's storms is currently pushing eastward as its currently sitting over the Northern Plains with light showers possibly sitting over Rapid city when viewed by Satellite. Some of those showers may move into Dawes county later tonight or possibly lose energy and dissipate before then. Pops over the northern half of Dawes county was kept at 18 percent or less to communicate the slight chance of these showers making it into Dawes county. A ridge begins to build into the Intermountain West later tonight to keep the forecast area temporarily dry for the next 24 hours. A low pressure system off the West coast is expected to stall over California but continually feed moisture into the Rocky Mountain Region. By the late afternoon to early evening time frame the first of a couple shortwaves is expected to impact the Rocky mountain region for some possible thunderstorm/rain shower chances. Our forecast area will have plenty of moisture to utilize by there is some uncertain on how strong the synoptic support will be to create the possibility of severe thunderstorms. The 12 and 15z runs of the High-res models only place around 500 to 1000 joules for areas east of the I-25 corridor. There's only a few lobes of vorticity thats expected between 00 and 03z Wednesday or Tuesday evening/night so the coverage may be very isolated as the synoptic support is kind of lacking underneath our weak ridge. To compliment the lack of unstable conditions, 700mb temperatures will range between 6 and 9C keeping the surface temperatures in the high 60's to low 70's to also help subdue any convective initiation during the day. However, looking at the Hi-res models composite reflectivity, some want to keep showers going through Wednesday morning before the Ridge takes back over to keep Wednesday relatively dry during the day.

LONG TERM /THURSDAY THROUGH MONDAY/

Issued at 338 PM MDT Mon Sep 21 2026

Southeastern Wyoming and Western Nebraska will be under southwesterly flow aloft as a mid-level ridge begins to build across the Central United States. With an embedded shortwave trough propagating across the region Wednesday afternoon combined with another surge of monsoonal moisture (PWAT again ranging within the 80th and 95th percentile), widely scattered showers and thunderstorms will be possible, mainly south of I-80. However, no severe weather is anticipated due to weak instability (MLCAPE ~100- 200 J/Kg) thanks to poor mid-level lapse rates. Temperatures look to be around or slightly warmer than average, in the low to mid-70s east of the Laramie Range and mid to upper 60s to the west. A weak cold front is progged to move through SE Wyoming and the W Nebraska Panhandle overnight Wednesday into Thursday, which may serve as a focal point for more shower development into the evening hours.

On Thursday, an additional shortwave trough within the longwave ridge pattern may result in another round of afternoon and evening showers and thunderstorms, with slightly cooler daytime high temperatures behind the front. With an effective bulk wind difference of only 15-20 knots along with relatively weak instability (MLCAPE < 500 J/Kg), no organized or severe weather is expected, despite a post-frontal air mass characterized by dewpoints in the low to mid-50s across the Panhandle and PWAT exceeding the 90th percentile yet again. This is rather rare for late September, but we will certainly take any moisture we can get despite nothing widespread expected...

The flow regime becomes more zonal on Friday which turns off our supply for the anomalously rich monsoonal moisture seen the previous days (PWAT ~0.9"). This will decrease our chances for any meaningful precipitation and will also be the start of a warming and drying period into the weekend. We will have to monitor increasing fire weather concerns into the weekend as long range ensemble guidance suggests gusty, westerly winds mainly across SE Wyoming, combined with daytime RH values of 20-25%. Not particularly concerned at this time as we are still short of critical fire weather thresholds, but will have to be monitored as we get closer given plenty of dry fuel and further warming underneath the building ridge. High temperatures this weekend look to be 5-10 degrees above average, perhaps reaching 80 degrees in areas east of the I-25 corridor.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 554 PM MDT Mon Sep 21 2026

Low clouds and areas of fog will be the primary aviation concern tonight. Widespread flight category reductions are expected for all terminals except RWL and LAR. For CYS and western Nebraska, expect at least MVFR, with high confidence in periods of IFR mainly between 08z and 15z at CYS, BFF, AIA, and SNY. LIFR is also likely at AIA and SNY, and possible at CYS and BFF. Confidence is a little lower in CDR reaching IFR conditions tonight (40% chance). There is some uncertainty in the timing of the initial flight category drop, and also whether CIGs will stay down or occasionally waffle back to MVFR or VFR. Look for gradual improvements Tuesday morning into the early afternoon from west to east. A few showers or storms may move into RWL by the end of the TAF period.

CYS WATCHES/WARNINGS/ADVISORIES

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