Riverton, WY Weather

Key Messages

- A weak disturbance pushes through the CWA Tuesday with isolated shower activity (<20%), mainly higher terrain west of the Divide.

- Above average temperatures continue through Thursday ahead of a cool down Friday and over the weekend.

- Increasing winds Thursday ahead of the next system with valley rain and mountain snow likely overnight into Friday and over the weekend. Totals of low confidence (~30%) but higher for impacts to mountain passes (50-60%).

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 for 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 4o 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

Issued at 950 PM MDT Mon Oct 19 2026

All terminals to be VFR through 06Z/Wednesday. The upper flow backs to the south-southwest Tuesday in response to a digging trough along the US West Coast. Mid-level moisture spreads north across far west Wyoming overnight and Tuesday morning, leading to isolated light showers within a BKN mid-level cloud deck. KJAC has a less than 30 percent chance of seeing a few sprinkles, mainly between 09Z-15Z/Tuesday. With the mid-level moisture in place, daytime heating helps to initiate convection over the western Wyoming mountains by early Tuesday afternoon. The chance of precipitation remains less than 30 percent with minimal impacts if a shower did move across a terminal. Terminals west of the Continental Divide, and perhaps KCOD, have the best chance at seeing a late Tuesday shower before sunset arrives. Other than a 4- to 6-hour period of 10-18kt winds at KCPR during the morning and early afternoon, wind speeds at all terminals should be less than 10kts through the period.

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

Riw Watches

None.