textproduct: Western and Central Wyoming

KEY MESSAGES

- Light snow/rain showers across portions of the state will gradually diminish through the afternoon and early evening today.

- Areas of fog linger over portions of western valleys such as Star Valley and the upper Green River Basin. Fog is expected to dissipate through the remainder of the afternoon/evening.

- Areas east of the Divide will see mild and mostly dry conditions prevail through the next few days.

UPDATE

Issued at 1205 PM MST Fri Jan 2 2026

A few things to update regarding the previous forecast discussion. The first being areas of patchy dense fog lingering across parts of western WY. Locations such as Star Valley and the upper Green River Basin will likely see fog linger through the afternoon into the evening. Visibilities of 1/4 to 2 miles are possible at times across the aforementioned area. Winter Weather Advisories have been cancelled early, due to most of the heavy precipitation having moved out of the area. A few isolated showers cannot be ruled out at times this afternoon/evening. Additional snow accumulations for western WY will be minimal with the highest elevations possibly seeing at most an additional 1 or 2 inches. The remainder of the forecast discussion has not changed with mild and mostly dry conditions prevailing across locations east of the Divide through the weekend. A second system looks to be on track to bring another round of snowfall to western WY and parts of southern WY as early as late Saturday night. Preliminary snow accumulations look to fall within the criteria for Winter Weather Advisories mainly across the western mountain ranges. However, at this time no winter highlights will be issued. Strong gusty winds still look possible early Sunday morning mainly along the wind corridor from Casper to Rock Springs. Currently winds look to be below high wind criteria but a few periodic gusty winds nearing 60 mph cannot be ruled out. Looking into next week there is the potential for a more active pattern with widespread precipitation chances other than western WY. However, models are very divided with little consensus among the top models. So at this time confidence is very low but it will be worth monitoring through the weekend into the start of next week.

DISCUSSION

Issued at 112 AM MST Fri Jan 2 2026

Light snow will continue in the Jackson and Star Valleys this morning, as the inversions that had been in place Tuesday and Wednesday held firm Thursday. This kept temperatures firmly below freezing through the day, in the middle 20s. Accumulations will remain light this morning, with low clouds/fog in place as well, with an additional 1 to 2 inches expected and the clouds/fog lifting/scattering out by midday. Moderate to heavy snow will also continue over the Tetons and Salt River Range this morning, with an additional 12 inches expected. Elsewhere in the western mountains, up to 4 inches will fall today. Isolated rain showers will continue across areas east of the Divide and southern portions this morning, gradually ending toward 18Z as a subtle shortwave traverses over the CWA and pushing the available moisture to the southeast. Temperatures are expected to stay above freezing in these areas and any possible patches of ice will be isolated. There is low confidence in temperatures rising above freezing in the western valleys today, as a transitory begins to build over the region this afternoon. This will allow for the inversion to reform and keep the cold air trapped in the valleys.

As was just mentioned, a transitory ridge will build back over the region during the day today, as a strong closed upper low moves over the EPAC toward the West Coast. Dry conditions and above normal temperatures will be in place across much of the CWA once again this weekend as a result (especially east of the Divide). A leeside trough will develop over eastern WY by 12Z Sunday, due to southwest winds aloft as the ridge transitions eastward. The timing for the strong to high winds looks to be shifted forward in time toward Sunday morning, as 700mb winds increase to 50 to 60kt over South Pass and southern portions of Natrona County. Any high winds (wind gusts 60+ mph) look to be brief during the day however, as winds look to be more west-southwest, as opposed to a more favorable southwesterly direction. The timing for the next round of snow has also shifted toward Sunday morning, as the first shortwave from the upper low looks to reach western portions by 12Z. Southwest flow aloft will continue Sunday into Monday, leading to a persistent flow of moisture. However, this direction is not as conducive for higher snowfall amounts. 700mb temperatures are forecasted to be around minus 4 to minus 6C (which corresponds to snow levels of 5500 to 6500ft), which will keep the precipitation as snow in the western valleys. Will have to see if this trend holds, as snow levels would be expected to rise in this flow pattern. Initial snowfall amounts Sunday through Monday look to be in the 6 to 12 inch range across the western mountains.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/

Issued at 1000 PM MST Fri Jan 2 2026

Most sites remain VFR through the next 24 hours with increasing high cirrus pouring in from the west. Fog is expected to be an issue at KBPI/KPNA again tonight, but will be a little later than last night. Expect fog to form 09Z/10Z and continue through midmorning. Light winds will keep fog from dissipating quickly. There are hints of fog at KJAC as well, but the signal for it is lesser, so have only brought a few hours at MVFR vis for the time being.

Light snow begins to move into KJAC after 00Z/04, but current timing for lower vis and cigs holds off until right at the end of current TAFs, so will start with VCSH for now.

RIW WATCHES/WARNINGS/ADVISORIES

None.