textproduct: Western and Central Wyoming

KEY MESSAGES

- A mainly dry and seasonable day today. A few showers are possible in southern Wyoming after sunset and into the overnight hours pushing as far north as the Winds by daybreak Wednesday morning.

- Increasing monsoonal moisture increases the chance of showers starting on Wednesday, with Thursday and Friday looking like the most active days.

- Temperatures will remain near to above average through most of the week, with a cool down likely for the weekend.

UPDATE

Issued at 1210 PM MDT Tue Sep 15 2026

Not much a short term forecast change as IR continues to show mainly clear skies and an empty radar through the rest of the day. Seasonable temperatures will be on a slight warming trend through the rest of the week into Saturday ahead of a cool down and regime change for Sunday into early next week. Otherwise, HiRes models continue to pump in moisture after sunset from the south that will spread northward overnight. Isolated shower activity and possible rumble of thunder up to the Winds by Wednesday morning but dissipates ahead of the afternoon. More isolated activity in the afternoon for point south of the Winds that will spread north into Thursday and Friday being more active, especially west of the Divide. Details uncertain on exact amounts, but much of the activity looks to be points west of the Divide and south of the Winds. Still isolated chances for points east and north but more limited on confidence (<20-30%) at this time.

DISCUSSION

Issued at 149 AM MDT Tue Sep 15 2026

The last two nights I used music to describe the weather of the day. So, why not make it three days in a row. Let's step back another decade today, to the 60s. And let us also change music genres again, this time to country. And this has to with a pattern that you would expect more during the middle of summer, not a week from the start of autumn. The song is by the late, great Johnny Cash, Ring Of Fire. Basically, a strong ridge sets up in the southern United States and moisture rides along the northern edge of it.

There continues to be a strong ridge over the southeastern and south central United States, bringing more record high temperatures. For us in Wyoming, we will be close to the top of the ridge, with an increasing chance of showers. For today and most of tomorrow, the bulk of the moisture looks to remain to the south of Wyoming. Just enough moisture will creep northward late today and especially tonight to bring some showers to the southern third of the state. But these still look fairly isolated and even here most locations should not see one (less than a 1 out of 4 chance). Moisture will try to creep further north on Wednesday but even on this day the bulk will remain south of the border with only isolated activity. As for temperatures, today looks fairly close to normal. With southerly flow increasing Wednesday, temperatures look warmer with highs rising to around 80 in some of the warmer spots.

Chances of showers should increase beginning Wednesday night and especially into Thursday and Friday. The ridge over the southeastern United States with retrograde toward the southern plains. At the same time, low pressure over the Pacific Northwest will begin to get pushed eastward. moving toward Idaho by Thursday night. This will push the plume of monsoonal moisture further north and west and into the Cowboy State. Precipitable water values could be rather high. The GFS has values approaching an inch, which is approaching 200 percent of normal Wednesday night and Thursday. This model does tend to overcook this somewhat, so reality may be closer to 150 percent of normal. Nevertheless, the chance of showers and storms will increase. Model guidance continues to have disagreements in the placement of the most numerous showers though. So, we have higher confidence in Thursday and Friday being the two more active days, but placement of the most numerous showers and precipitation amounts remains uncertain. Temperatures will remain somewhat above normal, although with more cloud cover a bit cooler than on Wednesday. And like most monsoonal events, all areas will have a chance of a shower or storm, but not everyone will see one.

There is more uncertainty for the weekend. There is still a decent model spread on how fast the low will exit the area. Most guidance now takes the low north of the area across Montana. With flow turning northwestward, Saturday looks like a cooler day across the area. How fast the low moves will determine the extent of any precipitation though since it will be of the wrap around variety. Most guidance favors northern Wyoming given the position of the low, with lesser chances further south. Sunday looks somewhat drier although a few areas may still see a few showers around. Ridging should build back over the area to start next week, bring a return to dry and seasonable weather.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 349 PM MDT Tue Sep 15 2026

Increasing moisture from the south brings increasing clouds overnight, though ceilings remain VFR. Best rain chances occur at KRKS, though models continue to be in a fairly large disagreement on placement and timing of rain showers, so confidence is low. Some lighter showers, or virga showers, may make it as far north as KBPI, KLND, and KPNA, but currently chances are too low to include in those TAFs. For Wednesday, diurnal winds increase for the afternoon, with shower and thunderstorm chances possible for the southern half of the area.

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.