textproduct: Western and Central Wyoming

KEY MESSAGES

- Any isolated showers will be confined to far west Wyoming and Yellowstone National Park overnight and Wednesday morning. Otherwise, dry conditions prevail.

- Daytime high temperatures remain around 8F to 16F above seasonal averages Wednesday and Thursday.

- A weather system begins to track into the region Thursday, as precipitation increases Thursday night across areas west of the Continental Divide. Rain and mountain snow persists through Friday night, with rain chances eventually spreading east of the Divide Friday evening.

- Strong southwest wind gusting 40 to 60 mph is expected on Friday within the Wind Corridor from Sweetwater County through Natrona County and into Johnson County. The wind then shifts to the north Friday night and Saturday behind a cold front.

UPDATE

Issued at 221 PM MDT Tue Oct 20 2026

Isolated showers will continue across western Wyoming this afternoon, mostly over the mountains. Not much change in the short term, with Wednesday and Thursday a little warmer and breezier as southwest flow increases ahead of the system mentioned below. This is still expected to bring rain and mountain snow to the area beginning Thursday afternoon. Latest guidance has decreased accumulations slightly; regardless, impacts are still mostly expected to be limited to the western passes. This system will also lead to strong wind east of the Divide on Friday as a surface low deepens to the north.

DISCUSSION

Issued at 130 AM MDT Tue Oct 20 2026

IR currently shows some increasing clouds pushing in from the southwest out of northern Utah and eastern Idaho west of the Divide. Some light shower activity will push in as well by sunrise Tuesday morning <20 percent in coverage that will continue through much of the day. Minimal QPF and no impacts are expected with this subtle mid level shortwave propagating up the L/W pattern. The main upper level low is currently off the northern California coast deepening with increasing divergence aloft and southward movement. This will continue to push south Tuesday, beginning its eastward migration come Wednesday that will be the next system to affect the northern Rockies and much of the CWA Thursday and beyond. The main finger of the PFJ continue to be well north stretching from the Pacific northwest and into southern Canada, keeping the aforementioned low cutoff from the meridional pattern for the the entire country.

A slight warming trend continues through Thursday ahead of this system, remaining about 5 to 10 degrees above average for this time of October but changes are incoming for Friday and beyond over the weekend and into the following work week. The low is trending to become more of an open and more progressive wave as it nears western Wyoming for Thursday. Ahead of this system, expect a tightening gradient about 5 to 7 mb difference across the state. Southwest winds will uptick up to 40 to 50 mph gusts, possible higher instances for the wind corridor of Sweetwater to Natrona Counties. Higher terrain of South Pass to Casper Mountain could push 60 mph with steering flow winds mixing to the surface under daytime heating of the afternoon.

As a cold front drops through late Thursday and into Friday, expect cooling temperatures dropping freezing levels down to 8-9kft. This will allow for mountain snow to develop late Thursday stretching into Friday and the weekend. Model trends continue to be fairly consistent on at least advisory level snow totals along and west of the Divide for the higher terrain areas. With the lowering freezing levels, expect impacts to mountain passes to include Teton and Togwotee for at least a couple inches. As the system progresses further northeast, expect the Bighorns to get the brunt of the snowfall that will likely see impacts to the Granite and Powder River passes. Stay tuned for updated forecasts and updates to any needed headlines in the coming days.

Valley rain will be more prevalent west of the Divide and basins to the east later Friday. Much of the area should at least see a chance for a bit or a cold rain, higher QPF amounts to the west due to the southwest to western flow of this system. Minimal accumulations expected east of the Bighorns being on the leeward side of this system. A second wave of the dipping jet stream come late weekend into early next week will reinforce the cooler, more fall like air with more mountain snow and valley rain to be expected if the longer term model solutions come into fruition. Being a week out, time will tell but the weather pattern looks to be changing and more active for the latter part of October as we inch closer to winter.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 950 PM MDT Tue Oct 20 2026

VFR conditions prevail at all terminals through the forecast period within southwest flow aloft. A mid-cloud deck accompanied by a few light showers traverses far west Wyoming, including in the vicinity of KJAC, between 10Z and 16Z/Wednesday. Little more than a few sprinkles expected from this activity. Another round could return to the far west for a few hours late Wednesday afternoon. Otherwise, generally scattered cloud decks through Wednesday afternoon. A surge of mid/high-level moisture approaches KRKS late in the period leading to lowering mid-cloud ceilings after 00Z/Thursday. At the moment, it appears precipitation remains south of KRKS. A few tricky surface wind forecasts for Wednesday afternoon. Differing solutions offered by hi-res models on when southerly wind mixes at KCPR and KRIW. Have tried to strike a balance on timing and direction, although the latest HRRR tries to hold the southerlies at bay a few additional hours at KCPR and altogether at KRIW. On the other hand, KRKS sees a 12-22kt southerly wind develop between 19Z-21Z/Wednesday and prevail until around sunset.

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

RIW WATCHES/WARNINGS/ADVISORIES

None.