textproduct: Western and Central Wyoming

KEY MESSAGES

- Mainly dry with well above normal temperatures through Monday.

- A gusty breeze will occur around Casper and in the Lee of the Absarokas through Monday.

- An approaching weather system may bring a widespread high wind event on Wednesday, with a period of heavy snow possible in the western mountains, and snow showers from southwest into southern WY.

UPDATE

Issued at 1044 AM MST Sun Dec 14 2025

No major updates with the forecast for today into tomorrow. Focus remains on the potent weather system arriving Tuesday, with widespread strong winds for Wednesday, and snow over western and southern Wyoming. The first signs of this system will be strengthening winds over the Absaroka and Wind River Mountains, with the potential for some strong downsloping winds from Cody to Clark Monday evening into Tuesday morning. Read the full discussion below for details on the midweek system.

DISCUSSION

Issued at 1240 AM MST Sun Dec 14 2025

It took me a while to graduate from college and become a meteorologist. I went to college, dropped out for a while, and eventually finished by going part time. And while I was out of college and when I was finishing up, I worked a variety of blue collar jobs. One was working in a factory that produced liquid packaging containers. Safety was obviously important there, as we were working with a lot of large and potentially dangerous machinery. And when working on these machines, we had to shut them down and lock the energy out. This process was called "Lock Out / Tag Out."

And this dovetails with one feature of the weather, in a rhetorical sense anyway, the wind which some call the Wyoming Wind Machine. Tonight, it is finally down for maintenance, and judging by the surface observations, with a nearly full lock out / tag out, at least in populated areas. However, the atmosphere is just about ready to begin removing the locks and powering up the machine. It will not be at full power at first, and only in select locations. However, toward the middle and end of the forecast period, we could be running at close to full power at times. Details will follow.

Flat ridging will be in place over the area for around the next 48 hours or so, bringing dry weather. Temperatures will remain above normal through this period as well with potential for some record highs, with some locations, like Buffalo, likely seeing highs in the 60s. The first place for the powering up of the wind machine will be the favored southwest flow locations, mainly from Muddy Gap through Natrona County and the leeside of the Absarokas. The 700 millibar winds only top out at around 35 knots though, so high wind is not expected. Conditions look similar on Monday as well.

Things begin to turn more active starting on Tuesday, as a Pacific trough and cold front approach the area. Some showers should begin to break out across western Wyoming as the system approaches. However, models have trended a bit slower so any amounts look light through this period. Wind will begin to increase somewhat on Tuesday, but mainly at favored locations. This will begin to change Tuesday night as a potent jet, possibly over 160 knots, begins to approach Wyoming. The first places to see the increase will be the favored prefrontal locations like the leeside of the Absarokas and from Muddy Gap through Casper, when we begin to see the first 50 knots barbs at 700 millibars show up.

The main event will be Wednesday into Wednesday night as the trough, front and jet cross the state. This is when all the locks on the wind machine are removed and it will likely be running at full power. If there is a silver lining with this system, it is that it will be a quick mover and would not persist for several days. However, this could be a notable wind event, even for Wyoming standards and even in places that are used to the wind. Looking at the GFS MOS, most locations have at least 30 knots sustained Wednesday or Wednesday night with several topping 40 knots. At Cody, it has 59 knots sustained for Wednesday night! This is the highest I have seen in my almost 14 years at this office. Now, this is usually overdone this far out so I don't expect anything as strong, but this definitely got my attention. In the probabilistic realm of guidance, things are also very impressive. Most of western and central Wyoming has at least a 1 in 2 chance of a peak wind gust of 55 mph. Much of the area also has at least a 1 in 3 chance of peak wind gusts over 70 mph, including Cody, Rock Springs, Riverton, Buffalo and Casper. The 700 millibar winds are also rather impressive, topping out at around 70 knots in many locations. Other rules of thumb are also indicative, with a 240 meter height gradient at 500 millibars across Wyoming (150 to 180 is usually sufficient for strong to high wind) and a 17 millibar pressure gradient from Gillette to Rock Springs (15 millibars is usually sufficient) at 06Z Thursday. The most likely time for this would be Wednesday afternoon into Wednesday evening as the jet moves through. Again, there is no certainty of this occurring but the chance is greater than 4 out of 5 as of now and this could be one of the more notable events we have seen in a while and needs to be watched closely.

There is also a snowy side to this system as well. This would mainly be in western Wyoming, since strong downsloping would keep areas further east mainly dry. The main time of concern would be during the day on Wednesday, mainly when the trough axis passes and the left front quadrant of the jet moves through. With the fast movement of the system, amounts should generally be under warning criteria, with only the southern Absarokas having at least a 1 in 5 chance of 12 inches of snow or more. The chances of over 6 inches are fairly good though, with a greater than 1 in 2 chance across many of the mountain ranges. Accumulations in the valley looks lighter though, with around a 1 in 4 chance of an inch or more, since 700 millibar temperatures starting at minus 3C would lead to a rain/snow mix at this start. Impacts across the passes could be substantial at times though, as the strong wind combined with the snow could likely sharply reduce visibility.

Following this, there may be a break for Thursday. Another system should approach for the end of the week, but details are impossible to hash out this far out given the strength of the Wednesday system.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 430 PM MST Sun Dec 14 2025

VFR conditions will persist through the period. The gusty southwest wind at KCPR will decrease slightly over the next couple of hours but remain elevated through the period. KCOD is expected to see a downsloping wind by 09Z tonight with frequent gusts to 20 knots through 18Z, increasing to 30 knots through Monday afternoon. Otherwise, wind will generally remain around or below 10 knots at other terminals, with a few to scattered high cloud deck.

Clouds will increase from the northwest late Monday afternoon with light showers over the western mountains and valleys before midnight as a weak disturbance moves through. MVFR conditions likely at KJAC from 16/02-06Z. The western WY mountains will become obscured Monday evening as well.

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

None.