Wyoming Starts December Warmer Than Normal, But Expect Snow By Christmas

There’s nothing like warm weather to start December. This week’s temperatures might not break heat records, but they will be significantly warmer than average for this time of year.

The National Weather Service (NWS) office in Riverton reports that temperatures across western Wyoming have been above average for months. That trend will continue this week.

“It’s not totally unheard of, but definitely a nice change from typical December weather,” said Joshua Rowe, a meteorologist with NWS Riverton.

While the month will begin warm, that doesn’t mean Wyoming won’t have a white Christmas, said Cowboy State Daily Meteorologist Don Day.

“From what I'm seeing, the white Christmas chances actually look pretty good,” he said. “It does look like the weather pattern is changing in the time frame of next week, probably through Christmas Week, so the opportunity to have snow on the ground on Christmas looks pretty good.”

High-Pressure Heat

The reason for above-average temperatures that will see highs in the 50s for parts of the state is a high-pressure system that will hang over Wyoming for the next week. Rowe said this system will keep things warmer and drier than average for the beginning of December.

“That's why we're seeing higher temperatures and a lack of precipitation,” he said. “We're not going to be breaking any all-time monthly records, but we don't have any accumulated precipitation until the next weather system comes in this weekend.”

Day said this is a direct result of the subzero surge of cold weather in the Midwest and Great Lakes. When it’s cold in the East, it’s warm in the West.

“When we get these cold outbreaks in the East, we’ll always be under high pressure and fair weather in the West,” he said. “The reverse is true, also. When we have bad, cold weather here, the eastern side of the nation has warmer, milder weather. That’s the way it works.”

Temperatures across Wyoming will range from the high 40s to low 50s for most of the week, depending on location. However, Rowe said it’s unlikely any records will be broken.

“It’ll be around 50 degrees in Lander and Casper on Thursday,” he said. “Lander’s record for Dec. 5 is 59 degrees, and Casper’s is in the 60s. There will definitely be above-normal temperatures this week, but they probably won't get that high.”

Eastern Wyoming started this week much colder, catching the edge of the subzero surge in the Midwest. Nevertheless, Aaron Woodward with the NWS Office in Rapid City, South Dakota, said temperatures will bounce back, too.

“Temperatures are going to rebound nicely, especially on Tuesday,” he said. “Gillette will be jumping into the mid to upper 50s, and the rest of the week will stay in the 40s. It’s going to feel pretty nice in eastern Wyoming.”

Michael Natoli with NWS Cheyenne described this week’s temperatures as “nothing too exciting.”

“Values in southeastern Wyoming will be about 15 degrees warmer than average for this time of year, but those records are pretty hard to beat,” he said. “I wouldn't call them extreme for this time of year, and we’re not forecasting any record highs this week.”

Little Coming Down

It’s not unusual for December to start warm and dry. Day said several above-average rebounds will likely happen throughout the month.

“There's going to be a lot of back and forth in December,” he said. “We’ll have periods like this, where cold weather comes down and shifts to the east, and we stay warm in Wyoming. This warm weather is great, but it doesn't necessarily mean it will be like this whole month. But we're going to have some ups and downs.”

High-pressure systems tend to keep things dry and calm, so the upside to a week of warm weather is that that wind won’t be so blustery. The downside to these ups and downs is that there isn’t much chance for precipitation next week, and there’s no snow in the forecast for the next several days.

“The current pattern is preventing any weather systems from pushing into the region,” Rowe said. “They're going to the north, up into Canada, and it'll remain that way for pretty much this whole week.”

Day isn’t flustered by the lack of frosty weather to start the rush to Christmas and New Year’s. It’s another opportunity for him to remind Wyomingites that we’ve entered the driest time of the year.

“The three driest months of the year on the plains are December, January and February,” he said. “Yes, it'll snow, and you can have the prairies covered in snow at this time of year, but if you look at the average precipitation, these are the three driest months. It’s just a dry time.”

Firey Fall

Meteorological fall runs from September through October, so December is the beginning of meteorological winter. The last few months were some of the warmest on record, or at least since records started.

Lake Yellowstone in Yellowstone National Park had an average temperature of 36.6 degrees between September and November, more than 3 degrees warmer than its average of 33.5 degrees. That makes it one of the warmest falls since recordkeeping began in 1998.

Rock Springs tied for the second warmer fall since 1948. The average temperature was 47.5 degrees, more than 3 degrees warmer than average.

Lander’s average fall temperature was 50.2 degrees. That was the second warmest fall in 133 years since record-keeping began in 1891.

“It was one of the warmest September we’ve experienced in recent years, and November temperatures weren't that far above average,” Day said. “October was the month that got it there. That was a month for the books in terms of warmth and dryness.”

These persistent above-average temperatures help explain Wyoming's disastrous fire season in 2024. More than 850,000 acres were scorched by wildfires, prompting Gov. Mark Gordon to allocate nearly one-third of his 2025 supplement budget for firefighting resources.

However, Wyoming’s meteorologists don’t see any foreboding signs in the warmer-than-average autumn. Every so often, that’s how fall falls in the Cowboy State.

“Sometimes it takes a little while for the cold air in Canada to filter down,” Woodward said. “We didn't get big, deep troughs pulling that cold air down this fall. But we are starting to see that pattern change, as we saw with this recent cold spell. That cold air is coming into our neck of the woods now.”

Cold Coming In

It’s a warmer-than-average start for Wyoming this December, but the extended forecast looks frostier.

“It looks like a cold system is moving in later this week,” Rowe said. “Dec. 7 and 8 will be our next chance of any accumulated precipitation, which means snow.”

By Saturday, western and central Wyoming could see a chillier change with some snow. Natoli said eastern Wyoming will wait a little longer, but the change is coming.

“The next cold front will end this warm pattern,” he said. “Saturday looks like another warm day before the cold front arrives. It could reach Cheyenne and Laramie by Sunday morning and almost certainly by Sunday night. There’s a little uncertainty on Sunday's temperatures, but we should be cooler by Monday.”

History is a helpful guide when it comes to seasonal weather. There are parallels to Wyoming’s current climate patterns that suggest plenty of winter ahead.

“This reminds me of the very dry year of 2012, a La Nina year like this one,” Day said. “We got out of that one, and it got wet again in 2013 and 2014. That'll probably be the case in this situation.”

Day is sticking to his long-range forecast for Winter 2024-2025. All signs suggested a colder, snowier winter for most of Wyoming, and nothing’s derailed that determination.

“It was certainly one of the warmer, drier falls we've seen in quite a while,” he said. “And these are above-average temperatures for the first week of December, but there's cold weather coming in.

‘White’ Christmas

As for that White Christmas outlook, Day's forecast depends on the definition. Some people want the landscape thoroughly covered with snow by Christmas Day, while others are happy to see a few flakes flying. 

"Is it a white Christmas if there's snow on the ground, or is it a white Christmas if it's snowing on Christmas? There's a big difference between the two,” he said. “I go with the latter because it's a bit easier to predict, and Wyoming is a big enough state that snow usually falls on Christmas Day. But the chances are better that there will be snow on the ground in some places this year.”

Andrew Rossi can be reached at arossi@cowboystatedaily.com.