Basin, WY Weather

Key Messages

- Shower chances (30-60%) are expected across south and southwest Wyoming through midnight tonight. Greater precipitation chances (40- 90%) arrive overnight through much of Friday for west and northwest Wyoming. Snow will largely be confined to the mountains.

- Strong gusty winds of 35 to 55 mph are forecast on Friday across the Wind Corridor, Bighorn Basin, Wind River Basin, and Johnson County.

- Low relative humidity values around 20 percent will result in near- critical fire weather conditions across Johnson County on Friday.

- Much cooler temperatures are forecast this weekend behind this weather system with near seasonable to below normal for this time of year.

Discussion

Issued at 100 AM MDT Thu Oct 22 2026

IR continues to depict ample cloud cover extending from the eastern Pacific, bringing in tropical moisture through much of the Rockies and pushing to the north. There has been a bit further eastern push of this moisture, and as such, any shower activity looks to be more along and east of the Divide extending from Sweetwater to Natrona Counties throughout the day Thursday. Impacts negligible at this time, brining in continued needed precipitation chances in the coming days. WV shows the main finger of the PFJ pushing further south across the Pacific northwest and extending into southern Canada. The closed low has pushed across southern California with its eastern progression starting as it nears the CWA and upper Rockies later Thursday. This will interact with the aforementioned tropical moisture that will provide better precipitation chances on Friday.

Winds will increase late Thursday morning as the gradient starts to strengthen ahead of this system, seeing southwest wind gusts up to 25 to 35 mph across the Wind Corridor, and 20 to 30 mph for other areas east of the Divide. 15 to 25 mph expected to the west, but the stronger wind comes late Friday morning and into the afternoon and evening hours. Winds remain elevated overnight Thursday, but the strongest winds up to 40 to 60 mph expected, highest from South Pass to outer drive of Casper Mountain, where an occasional higher gust is possible. Regardless, the main concern comes with frontal pass late Friday afternoon and into the evening hours out of the west to northwest behind it. Winds slowly diminish with the wind shift change but remain elevated for 2 to 3 hours behind FROPA before becoming relatively light overnight. Winds across northern Natrona and much of Johnson, will stay elevated through sun-up Saturday morning before becoming relatively light.

Precipitation wise, Thursday will see isolated shower activity, with the best chances for Sweetwater and Natrona Counties into the afternoon and early evening hours. A rumble of thunder cannot be ruled out with instability values up to 100-200 J/kg expected but much of this activity will be east into the CYS CWA. This will help aid the stronger winds as well with any outflows with this shower activity, but minimal impacts (if any) will be expected. Increasing chances come Friday morning with first wave of moisture coming out of eastern Idaho and northern Utah pushing into the west by sunrise. An isolated storm is possible with any stronger outflows the main hazard. Snowfall looks to be minimal for the highest of the peaks along and west of the Divide, through mid to late morning with dry conditions expected to the east. The next round of shower activity will come with frontal passage as the cold front pushes into Yellowstone by 3 to 5PM and pushing southeast and through the CWA by midnight. This is when freezing levels look to drop between 8-9kft, allowing for snow to fall across the higher terrain of the western mountains, and as well as the Bighorns. Minimal impacts expected for the Bighorns as models have diminished in QPF amounts, with the passes looking to stay minimally impacted at this time. West of the Divide will be a different story, even through less snowfall now likely. Teton and Togwotee has the best chances for a couple of inches to fall late Friday afternoon into the overnight hours (30-40%) with anything higher in elevation pushing up to 6 inches (50-60%). This could continue its downward trend, and as such, even advisory level snowfall does not look to be great at this time. This is following in line with last winter with systems that look good a few days out, looking to weaken as it nears the CWA before models do anything good on how it turns out. This could be a pre-cursor of the winter to come, especially with the stronger El-Nino expected as well.

As this more open wave progresses northeast and gets embedded back into the jet stream for the northern Dakotas, another trough begins to deepen along the Pacific Northwest out of the Gulf of Alaska with increasing divergence aloft. This begins to near the CWA by late Sunday and into early next week with a better track for the western mountains for any significant snowfall. Again, time will tell as we are finding out currently and from last winter. If anything, it will reinforce the colder air from this late work week system with more seasonable to just below average temperatures heading into the last week of October. In all, a more active pattern has commenced with more fall like weather as the jet gets closer and closer with its southward and standard progression (even if a month late).

Aviation

Issued at 430 AM MDT Thu Oct 22 2026

VFR conditions expected throughout the entirety of the period. Light winds and mid level clouds to start the period as shower activity increases at RKS after 20Z, pushing to CPR by 01Z for a few hour period of light rain and breezy winds. Highest wind gusts up to 25kts at CPR in the afternoon during peak heating and mixing to the surface with all other sites around 10kts and occasional 18kt gusts. The next round of precipitation pushes in from the west, first at JAC after 08Z, spreading to BPI/PNA by 09Z through the end of the period. The gradient tightens there after, with a possible stronger push of mountain air across LND during that time with HiRes models picking up on a 35kt gust. All other locations will start to see a stronger wind for Friday into the next TAF cycle as precipitation spreads eastward.

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

Fire Weather

Issued at 100 AM MDT Thu Oct 22 2026

Elevated fire weather concerns Thursday afternoon and early evening. Southwest wind gusts up to 25 to 35 mph across the wind corridor of Sweetwater to Natrona Counties, extending up to Johnson. Minimum relative humidity values, however, will remain above critical thresholds above 30 to 40 percent.

Stronger winds expected Friday afternoon, with southwest wind gusts up to 40 to 60 mph possible, highest across Sweetwater to Natrona Counties, to include South Pass to outer drive of Casper Mountain. Other areas east of the Divide will see wind gusts over 30 to 40 mph. Lowest humidity values will remain across eastern counties in the 20 to 25 percent, giving way to near critical fire weather concerns due to the strong winds.

The biggest concern, if any fires develop, will be a sudden wind shift by late afternoon through midnight as a cold front drops through the state northwest to southeast. Southwest winds will shift out of the west to northwest behind frontal passage with winds slowly diminishing behind it but remaining elevated into the overnight hours, especially for northern Natrona and much of Johnson Counties, before becoming relatively light by sunrise Saturday morning.