textproduct: Western and Central Wyoming

KEY MESSAGES

- A mainly dry start to the weekend today with temperatures remaining near to above normal for most.

- The next weather system approaches late tomorrow and tomorrow night the the next chance of showers, mainly East of the Divide.

- A gusty wind and low humidity may bring elevated to critical fire weather for Monday.

- We could enter a wetter pattern for later next week, although details on timing and placement of heaviest precipitation remain uncertain.

DISCUSSION

Issued at 125 AM MDT Sat Sep 12 2026

It definitely felt more like autumn when I came into work this evening. This was one of the first times I broke out my windbreaker since last spring. An we do have a gusty breeze this evening following the passage of a cold front. We still have a few light showers out there this evening, but nothing heavy.

Today looks like a rain free day for a vast majority of the area as much drier air passes in from the west, dropping precipitable water values to under a half an inch for most locations. The one exception will be across far southern Wyoming, mainly along and south of Interstate 80, where a bit more moisture will linger. We could see an isolated shower or thunderstorm here, but the chance is less than 1 out of 7 and therefore the POPs will be largely silent. Most locations should see a light to moderate wind today. Again, the exception will be Sweetwater County, where a gusty breeze will continue. And as for fire weather concerns, elevated will be likely but humidity should remain above critical levels. Temperatures will be cooler than yesterday, but still remain above normal for most. Northern Wyoming will be a bit cooler though, with places like Buffalo and Cody struggling to get above 70.

Moisture begins to increase tonight. Enough mid level moisture may return later tonight for a few isolated showers in the western mountains late tonight. The bulk of the moisture should hold off until late in the day and especially after sunset. The culprits for this will be a plume of monsoonal moisture moving in from the south, impacting areas largely East of the Divide. At this same time and upper level low will be moving northward from Idaho and into western Montana, dragging a negatively tilted trough and cold front through the area. And there could be some decent rain in eastern portions of the area. For factors for, we will have deep moisture, with precipitable water values approaching 175 percent of normal. The trough and cold front will also add some extra lift. The main factor against will be steering flow, which looks rather strong. There is generally 30 knots at 700 millibars with up to 50 knots at 500 millibars. So, any showers and storms will be moving at a decent pace. The main concern would be possibly training storms, or in southwesterly upslope areas, like the southern end of the Bighorn Range. The greatest chance would be largely along and east of a Kaycee to Rock Springs line, with lessening chances further north and west. And with the southwest flow ahead of the system, it will be a warm end to the weekend with many locations below 6000 feet well into the 80s for high temperatures.

Most showers should clear the area by sunrise on Monday, replaced by another cooler and drier airmass, with temperatures falling back toward normal levels. Concerns on this day shift to fire weather again. There will still be a decent height and pressure gradient between ridging over the southern United States and the upper level low moving into the Prairie Provinces. The result will be a gusty wind across much of the area. And with very dry air moving into the area, we will likely see at least elevated fire weather. The southern two thirds of the area; especially East of Rock Springs and Riverton, has at least a 1 out of 2 chance of relative humidity falling under 15 percent. We may need some fire weather highlights for this day, it is a bit too early to issue right now though.

Tuesday looks mainly dry at this point, although signs are pointing to another shot of monsoonal moisture starting to move into southern Wyoming for late Tuesday as another low moves toward the area. Most of the moisture looks to hold off until Wednesday though. A preponderance of the guidance takes this low more to the east and closer to the Cowboy State, bringing a better chance of showers for Wednesday and into Thursday and possibly into Friday as well. Details of precipitation amounts and timing of the heaviest precipitation remain in flux though as there are different solutions in regards to the exact timing and placement of the low. Nevertheless, we are looking at an increased chance of showers for later in the week.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 416 AM MDT Sat Sep 12 2026

VFR conditions should continue for a vast majority of the area through 12Z Sunday. The exception may be in vicinity of KCPR and KCOD this morning but cloud cover to the north has been largely low VFR instead of MVFR so we prevailed BKN040 with less than a 40 percent chance of MVFR ceilings this morning. A gusty wind will develop at terminals West of the Continental Divide after 18Z with gusts to over 20 knots possible at all terminals. Wind should decrease after sunset as the atmosphere decouples. There is around a 15 percent chance of a shower in the western mountain ranges after 04Z Sunday. Showers should stay away from TAF sites but could bring occasional mountain obscurations.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts.

RIW WATCHES/WARNINGS/ADVISORIES

None.