textproduct: Western and Central Wyoming

KEY MESSAGES

- More unsettled weather today with rain and snow showers continuing, especially across western Wyoming.

- A weather system will cross the area Thursday and Friday, bringing widespread snow and rain changing to snow. The highest amounts will occur in northern Wyoming, especially in the mountains with the highest amounts in the Bighorns.

- Mainly dry and mild weather returns for Saturday and lasts into early next week.

DISCUSSION

Issued at 256 AM MDT Wed Apr 1 2026

We have now entered April, and it is April fools day. For the past four months we have had what I would like the call a "Fool's Winter" for how mild and dry it was. We do need moisture badly. And, it is not an April Fool's joke that many areas will finally see some decent moisture. There will be a contrast between West and East of the Divide through Friday, and that is where we will divide the discussion.

West of the Divide...We do have some snow across the western mountains this morning as the next pulse of energy moves through the area. Much of the area should be in a lull during the day today as we will be in between systems, so additional amounts during the day should remain on the light side, with only a 1 in 5 chance of 3 or more additional inches in the Tetons and the Wind River Range. Relatively mild air will remain in place as well, with 700 millibar temperatures only falling to around minus 3, keeping snow levels above 7000 feet so valleys should see mainly rain.

Precipitation will begin in increasing tonight as an area of low pressure moves in from the west and increases moisture across the area. This will be a fairly long event, lasting around 42 hours from late tonight through Friday afternoon. With a greater than 1 in 2 chance of over a foot of new snow across the Tetons and southwestern Yellowstone, we have issued Winter Storm Watches for this area. We have also included the Salt and Wyoming Range and Wind River Range, but chances a bit lower here. I was on the fence of whether to issue or now. We went ahead an pulled the trigger for now. However, there is about an even chance these could end up being advisories as the position of the low would keep the heaviest snow across areas further north. For the Absarokas, most locations have less than a 1 in 5 chance of 12 inches or more, so no watches here, The only area with greater than a 1 in 2 chance is the far southwestern portion, and there are basically no roads or people in this area. As for timing, the heaviest snow should be Thursday night into early Friday as the low moves through with some wrap around upslope lingering through the day. Timing of the other periods of precipitation remains difficult though. As for the lower elevations, 700 millibar temperatures remain warm enough for rain until Thursday morning when 700 millibar temperatures fall and snow levels drop to the valley floors. Both the Jackson and Star Valleys look like borderline advisories right now, with around a 2 in 5 chance of 4 inches of snow or more. This would likely be on non-paved surfaces though, as the high April sun angle and warm ground would limit accumulation during the day. For any possible advisories, we will punt to future shifts for now. Further east in the Green River Basin, amounts should be small given the best moisture should remain to the north. Snow should taper off during the day Friday, with all snow over by sunset Friday.

In Sweetwater County, some energy will bring a better chance of showers today. It should remain in the form of rain except for the highest elevations, with 700 millibar temperatures remaining above minus 1, keeping snow levels above 8000 feet. The main concern for snow here would be later Thursday as cold air moves in as the low approaches. Amounts still look to remain on the light side though, with around a 1 in 2 chance of an inch or snow or more, mainly east of Rock Springs. The chance of 3 inches is less than 1 in 10 for all locations though. Gusty wind will accompany the showers on Thursday as well, but with 700 millibar winds only maxing out at 40 knots, high wind is unlikely.

East of the Divide...Not much change here. Temperatures will be close to somewhat below seasonal normals. There will be some showers around as well but most locations should be most of the time. Most guidance gives the best chance of more numerous showers to Natrona County, but the showery nature of the precipitation makes pinpointing it difficult. There could even be a bit of freezing drizzle across the northern Big Horn Basin early this morning, largely before sunrise.

Much of Wednesday night and Thursday morning should be largely dry before the main event begins as the low moves into Wyoming, most likely crossing the center of the state. There will some decent wind ahead of the low, mainly across the favored southwest flow areas from Muddy Gap to Casper. The 700 millibar wind only tops out around 40 knots though, so high wind is not anticipated. With the movement of the low, the focus of most of the moisture across northern Wyoming, largely north of the Owl Creek and Bridger Ranges. Most precipitation should remain in the form of rain before the cooler air moves in late in the day and at night, changing precipitation to snow from west to east Thursday night, with the heaviest snow falling from late Thursday night through mid afternoon on Friday. As for snowfall amounts, in the lower elevations the rule looks to be some for almost everyone but not a lot. Most locations have at least a 1 in 2 chance of 1 inch of snow of more, with the exception of the Wind River Basin. As we move up to 3 inches, which is advisory criteria, the pattern favors areas with favorable northwest flow. The areas with a greater than 2 out of 5 chance (and the best chance for advisories), include Johnson County, Natrona County as well as Hot Springs County and Washakie County around Ten Sleep and further southeast. The chance of 6 inches or more is generally less than 1 out of 4, so the chance of any warnings at this time is low. The one area that may have a chance of a warning is Johnson County, where a gusty to strong wind may accompany the snow with the northwest flow / cold advection behind the low and bring lower visibility with the blowing and drifting snow.

However, there is one area that has the potential for a good amount of snow, and that is the Bighorn Range, especially the western slopes. This a very good set up for heavy snow, especially after the low passes later Thursday night into Friday as a moist, wraparound, northwest flow develops. Areas north of Powder River Pass have at least a 1 in 2 chance of 12 inches of snow through the duration of the storm. The far northwestern portions of the Bighorns even have a 1 in 2 chance of 20 inches or more. Needless to say, the passes going over Bighorns will be impacted during this period.

Starting on Saturday, quieter weather should return to the area. Temperatures will remain cool on Saturday as snow melts. Flat ridging should control the weather through at least Monday, bringing dry conditions and above normal temperatures, but not as warm as we saw in March. The next chance of precipitation may arrive the middle of next week as another Pacific system approaches.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 525 AM MDT Wed Apr 1 2026

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

A system will continue to impact the area today, leading to MVFR to IFR conditions at terminals for much of the period. The morning will bring the most widespread impacts, especially with ceilings. The afternoon hours will see less persistent impacts at terminals as precipitation becomes more scattered and transitions to all rain. This wave will move out around 00Z, bringing a short break before the next system pushes into western Wyoming. This will return IFR conditions to KJAC, KBPI, and KPNA after 08Z Thursday.

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

A system will continue to impact the area today, leading to periods of MVFR to IFR conditions at terminals. With precipitation falling as rain, lower ceilings will be the most widespread impact. However, confidence has generally decreased on persistent, prevailing impacts this afternoon as rain becomes more scattered, and have gone with TEMPO or PROB30 groups at several terminals. Rain decreases after 00Z Thursday as this wave moves out, with the next wave bringing more precipitation chances and lower ceilings around or after 12Z.

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

RIW WATCHES/WARNINGS/ADVISORIES

Winter Storm Watch from this evening through Friday afternoon for WYZ001-012-014-015-024.

Winter Storm Watch from Thursday evening through Friday afternoon for WYZ008-009.