The polar vortex that swept across Wyoming this weekend dumped heavy snow in the mountains. And by a lot, we mean a lot.
A monitoring station above Centennial in the Snowy Range recorded 65.5 inches of snow in 40 hours. Another monitoring station on the west side of the Snowy Range recorded over 75 inches over the same period.
That doesn't mean there's 66 inches of snow covering Centennial. The National Weather Service (NWS) hasn’t posted official totals yet, but there was at least a foot and a half of snow covering the community by Monday morning.
"The Snowy Range and Sierra Madres got clobbered," said Cowboy State Daily meteorologist Don Day. "The amount of snow they got between Thursday and Monday was very impressive."
If Wyoming gets a few more systems like this before the end of December, it could make up for the no-snow November. Regardless, more snow in the mountains is good news.
"One thing I've learned is that if you give Mother Nature time, she even things out," Day said. "That means patience, which is a virtue, but the last five days are a response to the warm, dry November."
How Much Vs. How Much
There are hundreds of monitoring stations and sensors in Wyoming's mountain ranges. They provide accurate information on the depth of the accumulating snowpack.
"Those sites are designed to estimate the amount of snow based on the weight and water content in the snow," Day said. "When there's a big snow event in the mountains, the NWS takes that information and applies what's called a snow ratio formula."
The snow ratio formula is dependent on temperature. When an inch of water is collected during a snowstorm with temperatures of 32 degrees, that's approximately 10 inches of snow. Meanwhile, an inch of snow in a 20-degree snowstorm would be closer to 25 inches.
"That's the physics of snow at different temperatures," Day said.
The metric that Wyomingites will find most reassuring is how much the snowpack percentages changed over the weekend. Day said there was a noticeable increase thanks to the influx of wet, heavy snow.
"I saw a snowpack increase of over 30% in four days," he said. "We have a long way to go, but that's a significant boost from a low number."
Downslope Battle
Many of the monitoring stations and sensors are associated with the community they're closest to. That doesn't mean Centennial got 65 inches of snow this weekend, but the higher peaks in the vicinity got that much and then some.
Day said the weekend snowstorm wasn't favorable for Centennial to get smothered by snow. Despite the snowfall in the mountains, the winds weren't favorable for heavy snow on Centennial's side.
"The pattern that brought big amounts of snow had winds that carried moisture from the northwest, and they moved southeast," he said. "That's a good direction for Wyoming's southern mountains to catch the moisture, but not the right setup for Centennial."
Centennial sits on the downslope of the eastern side of the Snowy Range. As the storm is caught in the mountains and travels downhill, it loses much of the moisture it was carrying.
When storms move in from an easterly direction and head upslope, that's when Centennial gets covered in snow. That can happen during the winter, but this weekend's snowstorm wasn't in the right position.
"They'd need the wind to be different, and that needs an entirely different scenario than what we experienced," Day said. "It's all about topography and wind direction with these storms."
Parched Plains
There were large amounts of snow recorded in most of Wyoming's mountain ranges over the weekend. As is often the case, the high places get more snow than the low places.
But what about the plains? There hasn't been more than a sprinkling of snow across Wyoming's lower elevations this season.
Day said this weekend's snowstorm is more typical for a Wyoming winter, especially in December. According to Day, snowstorms tend to favor the mountains or the plains, but rarely both.
"What's good for the mountains is not necessarily the best situation for the low elevations," he said. "I remind people about this all the time, and this weekend was a good example. The mountains got hammered, but most of us didn't see much out of that storm. When you get snow on the plains, places in the mountains you'd expect to be covered in snow haven't gotten any."
To get snowstorms that favor the lower elevations, Day said the all-important winds aloft need to come from a different direction, primarily northerly or easterly as opposed to the dominant northwesterly direction.
Of course, the mountains don't help. Elevation can take a lot out of a promising snowstorm.
"The more the air has to rise, the more gets squeezed out of it," Day said. "That's why the west-facing, upwind slopes always get the most snow, and why this storm was so productive for the mountains."
What Wyoming Wants For Christmas
November was warmer and drier than many would have hoped. The weekend's snowstorm gave the mountains a nice boost, but the plains are still dry and bereft.
Day referenced one of his oft-stated facts of Wyoming's winters. There will be more snow in the coming weeks, but this is, historically, the driest time of year for the Cowboy State.
"The two driest months on the plains in Wyoming are December and January," he said. "February and March are when you see the shift toward bigger snowstorms in the lower elevations. There are exceptions, but December and January are the important months for the mountains."
Day said, historically, Wyoming's more likely to have a White Halloween than a White Christmas. Still, Day is among those hoping for similar storms before the end of the year.
"If we get a couple more of these storms, we'll make up for November," he said. "It's still early in the winter season, but I'd like to see two or three more events like this before the end of the month, and I think there's a chance for a couple more, at least."
In the meantime, Centennial can enjoy being Wyoming's best winter wonderland of the season, so far. There should be plenty more where that came from.
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
