textproduct: Western and Central Wyoming

KEY MESSAGES

- A warm day today with a gusty breeze developing and possible elevated fire weather in the afternoon.

- A weather system lifts northward across the area tonight, bring some showers and thunderstorms along with areas of strong wind.

- A combination of a continued gusty breeze and low humidity may bring critical fire weather to portions of Fremont, Natrona and Sweetwater Counties Monday afternoon.

- A chance of showers returns from Wednesday through Friday, although details of timing and placement of the heaviest showers remain in flux.

DISCUSSION

Issued at 218 AM MDT Sun Sep 13 2026

Some people who read my discussions know that I like the reference old song lyrics to compare to the weather. And today's reference is another 1980s song, Madonna's second hit, "Borderline". In the song, she talks about pushing her love over the borderline. In the weather, the question is whether or not the weather can cross the borderline into needing highlights. And we have two of these dilemmas this morning.

The borderline conditions are not today for the most part though. Today will be a warm late summer / early fall day across the area. An approaching cold front and a trough axis will tighten the pressure gradient across the area, and bring a breezy to windy afternoon across the area. Temperatures East of the Divide will rise well into the 80s, with a few of the warmer spots possibly getting close to 90. As for fire weather, critical fire weather does not look likely as dew points will be rising ahead of the front, although some locations will see isolated fire weather at times this afternoon. As for the chance of precipitation, the morning looks generally dry. The one fly in the ointment is the European model does have some light showers over the far northern and eastern areas before noon. However, this model is the outlier and even the this model is further east than the 12Z run. So, we kept the forecast dry for now, but a 10 percent chance of a shower is still possible. A few showers and thunderstorms will break out this afternoon, but the bulk of the activity should hold off until this evening.

All guidance shows a chance of showers tonight, with the best chance in southeastern portions of the area. Many areas will have a chance though. There is still disagreement in rainfall amounts though, especially with the convective nature of the precipitation. As for flooding potential, there could be some locally heavy rain but with strong steering flow, showers and storms will be moving so the threat looks minimal. This is where we reach the first borderline situation. And this is for the potential for high wind. We do have one of the indications for high wind across portions of the area, we do have some 700 millibar winds of 50 knots. There will also be a decent jet streak moving in, around 100 knots this evening. There are some indications against it though. For one, it looks like a brief period of higher wind aloft, generally less than 6 hours. Also, ensemble guidance, both the HREF and NBM ensembles, gives less than 1 in 3 chance of wind gusts over 55 mph except in the mountains. The one location I am most concerned about is the Cody Foothills, where there are some indications of a possible mountain wave or gap flow, especially between midnight and 5 am. The best chance of this would be near Clark, where criteria is higher. We will hold off on any wind highlights for now and let the day shift take another look. Any showers should end by shortly after sunrise on Monday.

Then we move to Monday, where we have our other situation of borderline highlights. The 700 millibar wind will remain strong, but will gradually decrease through the day as the jet streak moves away. The borderline situation is potential Fire Weather. Areas like Natrona and Sweetwater County will have the wind, with a greater than 4 out of 5 chance of wind gusts over 30 mph through the day. Humidity looks borderline though. Further west in Fremont County, the humidity will be plenty low. However, wind looks more borderline with only a 1 out of 2 chance of wind gusts over 30 mph. Also, if there is a decent amount of rain in Natrona County, it could wet the fuels. However, it has been very dry. And, with thinking that fire weather is the greater threat than high wind, we have issued a Fire Weather watch for the above mentioned areas. It will also be a cooler day behind the front, with high temperatures 10 to 15 degrees less than on Sunday.

Tuesday looks like a dry and seasonable day across most of the area with less wind. A bit of moisture may come far enough north for another chance of a shower or thunderstorm across Sweetwater County. And, much like yesterday. Wednesday into next weekend remains in flux with a lot of uncertainty. The main driver this far out will be an upper level low that will be located over the Pacific Northwest on Wednesday. The models continue to struggle with its movement, especially the European which has trended slower and further north. At this point, it looks like there will be a chance of showers and thunderstorms each day from Wednesday through Friday. However, confidence in picking a more active day and especially pinpointing the most numerous showers remains very low. So the forecast is subject to change in the extended portion of the forecast. And with the southwest flow ahead of the low, temperatures should rebound to above normal levels once again for later in the week.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 420 AM MDT Sun Sep 13 2026

Largely VFR conditions should continue through 12Z Monday. Wind will start off light to moderate but a gusty southwesterly wind will increase through the day as a weather system approaches the area from the south. Gusts to 20 knots are possible at most terminals this afternoon with the exception of KCOD and KWRL. There is around a 20 percent chance of a shower in vicinity of KCOD until around 15Z this morning, and a 30 percent chance of a shower or thunderstorm in vicinity of KRKS after 23Z. Otherwise, dry conditions are expected at the TAF sites through the daylight hours.

Strong wind may develop tonight in the Lee of the Mountains East of the Divide, mainly in vicinity of KLND and especially KCOD, with gusts to 35 likely after 04Z. There continue to be some indications of a possible mountain wave near KCOD after 06Z, but still some uncertainty if the wave can reach the airport or remain to the west. Strong gap flow remains possible. Downslope flow will be the reason for the strong wind at KLND. Some showers will spread into the area tonight. The best chance of showers will in the eastern and southern terminals, mainly in at KRKS and KCPR.

FIRE WEATHER

Issued at 218 AM MDT Sun Sep 13 2026

A gusty afternoon breeze may bring some elevated fire weather this afternoon. The main concern will be on Monday, when a combination of a very day airmass with humidity under 15 percent and a gusty to strong southwest wind may bring critical fire weather Monday afternoon, mainly in Natrona, Sweetwater and Fremont Counties. Elsewhere, elevated fire weather is possible but critical fire weather chances are less than 40 percent.

RIW WATCHES/WARNINGS/ADVISORIES

Fire Weather Watch from Monday afternoon through Monday evening for WYZ279-280-283-289-300.