textproduct: Western and Central Wyoming

KEY MESSAGES

- Breezy to windy condition across parts of the state today with light snow increasing in coverage over western WY this evening.

- The first significant snowfall for the mountains of western WY is on final approach. Periods of light to moderate snowfall will be possible tonight through Saturday afternoon across the lower elevations with moderate to heavy snow expected for the western mountains.

- Widespread breezy to gusty winds are expected Friday afternoon through the overnight hours. Gusts of 25 to 35 mph will be common across the Wind Corridor with wind prone locations seeing gusts around 50 mph.

- The upcoming week looks to see mild and dry conditions return to eastern WY with active weather possibly continuing across the west.

UPDATE

Issued at 108 PM MST Thu Dec 4 2025

The overall forecast remains for the most part on track with only a few slight adjustments. Firstly, temperatures today will be near seasonable west of the Divide and on the warmer side of seasonable east of the Divide. Highs will range in the mid to upper 30s with some locations nearing 40 east of the Divide, temperatures west of the Divide will be cooler mainly around the upper 20s. Gusty winds have arrived at some locations this afternoon with gusts of 40 or more mph already occurring at Cody and Rock Springs. The upper Wind River Basin is also seeing some gusty winds currently with gusts of 30 to 40 mph. These winds are forecast to weaken slightly overnight but still remain windy through the overnight into Friday.

As for the next few days the main focus continues to be the incoming system which will bring rounds of moderate to heavy snow across western WY. The previous discussion still does a good job of explaining the setup along with the timing of the system. Overall the forecast remains mostly unchanged with the only deviation being a slight shift in snowfall amounts. Western mountains are still expected to see anywhere from 10 to 20 inches with the higher elevations seeing 2 to 3 feet. As more hi-res models become available it seems there has been a slight increase in snowfall amounts across the Bighorns. Amounts look to have increased in coverage with much of the range north of Powder River Pass forecast to see 10 to 18 inches now. The other shift is over lower elevations of western WY this includes Jackson Hole, Star Valley, southern Lincoln County, and the upper Green River Basin. These locations have seen snowfall amounts drop slightly compared to overnight. A likely reasoning for this is the warmer temperatures that will be present Friday and Saturday. Forecasted temperatures at times may be flirting with the freezing mark with portions of Jackson Hole possible getting into the mid 30s. However, even with these slightly warmer temperatures, precipitation is still expected to fall as snow but accumulation may be hindered at times. Storm total amounts for these lower elevations look to range from 5 to 10 inches with lesser amounts of 1 to 4 inches nearby Pinedale and over southern Lincoln County. Winds increase during the afternoon/evening Friday across much of the state. This increase in winds combined with snowfall will likely make travel very difficult over portions of western WY Friday night through Saturday morning. Besides western WY, winds are forecast to increase east of the Divide with widespread gusts of 35 to 45 mph along the Wind Corridor from Casper to Rock Springs. An isolated snow shower or two may be possible Friday night through Saturday morning with most expected to remain dry. No additional winter highlights have been issued or changed.

DISCUSSION

Issued at 343 AM MST Thu Dec 4 2025

10Z water vapor imagery shows strong north-northwest flow aloft with ridging over the Pacific and a broad trough to the east. An embedded weak disturbance is entering the northwest portions of the state. This will provide weak support for orographically-induced light snow chances (20%-40%) across higher elevations of Yellowstone National Park and the Teton Mountains through just after sunrise. Some breezy 20 to 30 mph winds will also be present from Rock Springs to Casper as the weak disturbance traverses the state through the morning. Seasonal temperatures are forecast today ahead of the incoming weather system.

By the early afternoon, the first "wave" of this multi-day snow across the west and widespread gusty winds will approach. This first wave, currently (10Z) moving onshore over the Pacific Northwest, will mostly be a wind maker across the Absarokas (including the Cody area) , upper Wind River Basin, and across the Wind Corridor. This wind will be a result of a tightening pressure gradient ahead of the second "wave" and associated cold front later tonight. Gusty winds of 30 to 35 mph will be common across the aforementioned locations, with isolated gusts of 50 mph possible. Snow with this first wave will be confined to western Wyoming. Snow amounts this afternoon (from 11AM to 5PM) are forecast to be up to 0.5 inch across Jackson and Star Valleys and much of Yellowstone. The Tetons and high elevations of Yellowstone could see around 2 inches during this time frame.

The second wave begins around sunset tonight as upper level divergence is enhanced over western Wyoming, thanks to being in the left exit region of a 125kt-150kt upper level jet. With abundant moisture filtering into the region and enhanced lift, due to orographics and upper level divergence, moderate to heavy snow is expected from sunset tonight through early Friday morning for the western mountains. During this time frame, snow amounts across the Teton, Gros Ventres, Salt River, and Wyoming Mountain Ranges and high elevations of Yellowstone range from 6 to 12 inches. As for the western valleys and low elevations of Yellowstone, snow amounts overnight tonight generally range from 1 to 3 inches.

A lull in moderate to heavy snow is currently forecast between sunrise and midday Friday as the upper level jet shifts east over Wyoming. However, light snow will likely (90% chance) be falling during this time. Once the 125kt-150kt jet is overhead, the third wave begins early Friday afternoon and continues through Saturday morning. During this time, moderate to heavy snow is forecast across most of western Wyoming. Snow totals across the Teton, Gros Ventres, Salt River, and Wyoming Mountain Ranges range from 1 to 2 feet with the highest elevations seeing 3 feet. Thus, the Winter Storm Watch has been upgraded to a Winter Storm Warning beginning 5PM tonight and continuing through 2PM Saturday. Travel over Teton, Togwotee, and Salt River Passes could become very difficult, especially during both "waves".

Winter Weather Advisories have also been issued for the Upper Green River Basin, the western Wind River Mountains, the Absarokas, Yellowstone, and Jackson and Star Valleys. Total snow amounts of at least 7 inches (80-90% chance) are forecast for Jackson and Star Valleys, Yellowstone, and the Upper Green River Basin. For these locations, the probabilities of at least 8 inches ranges from 40% to 80% over a 40+ hour period so opted only for Winter Weather Advisories at this time. Higher elevations of Yellowstone (Pitchstone Plateau) could see upwards of 2 feet, however, because these areas are largely untraveled, kept with the Advisory. Similar thinking swayed the thinking for the western Wind River MOuntains, the Absarokas, and the western Bighorns, with snow amounts between 8 and 12 inches. Locally higher amounts are possible (70%) across the highest elevations of these mountain ranges. It is important to note that gusty winds look to accompany the moderate to heavy snow, leading to reduced visibilities.

With the strong upper level jet moving overhead Friday afternoon, winds begin to ramp up across the Wind Corridor and the Absarokas with frequent 25 mph to 35 mph gusts. This will likely (80-90% chance) translate to frequent gusts of at least 35 to 40 mph. Wind prone locations, such as South Pass and Muddy Gap, could potentially (50-80% chance) see gusts around 50 mph. Gusty 30 to 40 mph drainage winds across the upper Wind River Basin look to develop (90% chance) late Friday into Saturday as well. As the jet moves overhead, 700mb winds of 50kts to 60kts are forecast to develop over southern Wyoming, the Absarokas and the Upper Wind River Basin late Friday evening into the overnight hours. There is a 50% chance for wind gusts 60+ mph to occur in these areas as a result of the jet max moving overhead and mixing these stronger winds to the surface. Similar conditions look to develop through the rest of the Wind River Basin and northern Johnson County between 09Z and 12Z Saturday. These potentially high winds could last through Saturday morning, before gradually decreasing after 21Z Saturday.

The upper-level jet begins to weaken and shift south during the day on Saturday, bringing an end to the impacts of the winter system. Ensemble guidance is in consensus that the northwest flow will persist Sunday into the early parts of next week, allowing for light snow to chances (30-80%) continue across the west. Elsewhere, dry conditions and a warm up to above normal temperatures is also looking more favorable.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

Issued at 954 PM MST Thu Dec 4 2025

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals.

Snow will continue through much of the night at KJAC, with IFR persisting through at least 16Z Friday. 20 to 40% chances continue to exist that KBPI and KPNA will also see some snow showers during the night, with KPNA being the more likely terminal to see those snow showers. MFR conditions would be expected if those snow showers occur. A wave will also bring snow showers northward near KRKS early in the period, and could last through much of the night. Occasional IFR conditions are possible as a result. Most models are indicating a lull in snowfall Friday afternoon, which could bring KJAC up to VFR, however, given westerly flow and orographics, expect KJAC to remain MVFR during the lull. A much heavier period of snow is then expected beginning around 23Z Friday afternoon at KJAC which will last through the rest of the period. Expect IFR to LIFR conditions through much of the night as a result. This more potent push of snow looks to impact KBPI and KPNA (70% chance) as well as KRKS (50% chance) late in the period. It should also be noted that gusty winds will also accompany the snow at KRKS, with gusts 25 to 30kts through much of the period. This could lead to blowing snow, especially after 02Z Saturday.

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals.

With the approaching weather system, wind will be the main concern east of the Divide, though winds will continue to decrease to start the period with most terminals seeing winds dropping below 10kts by the start of the period. The exceptions are KCPR and KCOD, where gusts around 20 to 25kts may linger for the first 2 to 3 hours of the period. Midlevel cigs also will be expected overnight for most terminals. There is a slight chance of seeing some snow showers out of those lower cigs, with most likely chances at KWRL (30% chance) but KCPR (20% chance) and KCOD (10% chance) may also see occasional snow showers. The mid-level cigs should filter out by midday Friday, with BKN to SCT high clouds remaining and continuing through the end of the period.

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

RIW WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 2 PM MST Saturday for WYZ001-002- 008-013-014-023-025.

Winter Storm Warning until 2 PM MST Saturday for WYZ012-024.