Enjoy the unseasonably warm April weather while it lasts, because it’ll be gone by Thursday.
A slow-moving cold front will move across Wyoming between Wednesday night and Friday. When it does, temperatures will drop up to 50 degrees in some places, and the entire state will get some snow.
“At this time of year, you can see the pendulum swing from one direction to another very quickly,” said Cowboy State Daily meteorologist Don Day. “We’re going to see equal but opposite extremes in temperature on Thursday and Friday, and just about everyone's going to see snow.”
Pendulum Swings
Day categorized the incoming cold front as “a true taste of winter” returning to Wyoming. That’s not uncommon in April, but the intense reversal will catch a lot of Wyomingites off guard.
“Last week, we had temperatures in the 70s and 80s,” he said. “This Friday, temperatures will be more than 50 degrees colder in places. I'm looking at 32 degrees in Cody, 28 degrees in Cheyenne and 25 degrees in Laramie. And those are the highs.”
Thursday night and Friday morning temperatures could be in the upper teens and lower 20s, and Day wouldn’t be surprised to see subzero temperatures in Yellowstone National Park.
However, Day wouldn’t categorize this as an extreme switch, especially during a historically volatile month like April. It’s just the luck of the draw in Wyoming.
“One thing about Wyoming is that we're situated to be affected by air masses from much different source regions,” he said. “¥ou get air out of the deserts today and tomorrow, followed by air out of the Pacific Northwest on Thursday and Friday.
“Sometimes, those air masses switch in less than 24 hours. But the pendulum swinging is normal in April. People talk about what the normal highs and lows should be, but all normal are averages of the extremes.”
When It Snows, It Pours
Between Wednesday night and Friday, nearly all of Wyoming will see some precipitation, probably in the form of snow. However, there’s still some uncertainty about how much precipitation will fall and the proportion of wet snow to cold rain.
“The precipitation moving in with the front may start as rain in some places, or may be all snow in other places,” said meteorologist Celia Hensley with the National Weather Service office in Riverton. “The biggest question mark with this forecast is how intense will it be snowing.”
Hensley said there could be some snow accumulation depending on ground temperature. Snow is expected to start sticking on grassy surfaces, but it could get cold enough to form on roads and highways, especially overnight.
“With temperatures right around that freezing mark, the precipitation should mostly be snow,” she said. “However, given our recent warmth, the time of year, and sun angle, impacts to travel on roadways during the daylight hours should be minimal. Higher elevation areas like mountain passes, Wind River Canyon, and Casper Mountain will be impacted more than lower elevation areas.”
Between Wednesday and Thursday, the entire state of Wyoming could receive up to half an inch of precipitation, rain, or snow.
According to NWS Riverton, communities like Cody, Casper, Buffalo, and Riverton have an 80% to 95% chance of getting over an inch of new snow by Saturday. Lander, meanwhile, has an 85% chance of seeing over four inches of snow during the same period.
“We're looking at anywhere from three-tenths of an inch of moisture on the low end,” Hensley said. “Some places, especially in the mountains, may see up to an inch of moisture.”
This is one of those cold fronts where a few hundred feet could make all the difference. Hensley said it will be entirely dependent on air and ground temperatures once the snow starts to fall.
“What could be rain or light, misty snow in downtown Riverton could be heavy snow at the NWS Riverton Office, 500 feet higher up,” she said. “A few hundred feet of elevation could make all the difference in snowfall and whether it's accumulating on roads.”
Will It Be Enough?
Michael Natoli with the NWS Office in Cheyenne is anticipating the “abrupt end” of the warm weather Wyoming has been enjoying for the last two weeks. The cold front should bring its full brunt to southeast Wyoming by Thursday evening.
“We may see some rain showers right at the beginning, but we expect this to transition to snow pretty quickly,” he said. “Amounts are still uncertain, but there is a potential for some accumulating snow, even in the valleys.”
The big question is whether this weather system will be enough to alleviate the drought gripping the southeast corner of Wyoming. Natoli said every drop of moisture is welcome, but the monthly threshold has yet to be reached.
“We’re headed into our wettest time of the year, but just one of these storms is not enough to dent the drought,” he said. “In Cheyenne, the average liquid precipitation in April is close to two inches through the month. So far, we have received essentially nothing. Half an inch of precipitation from this storm is the most likely scenario right now, which is a good amount, but we have a ways to go to make up the long-term deficit.”
Meanwhile, daytime highs in southeast Wyoming will be in the 20s and 30s. There’s no escaping the impact of this winter weather system.
“It’s going to cool down pretty quickly,” Natoli said. “This is going to be a pretty cold storm.”
Morning Warning
The consensus among Wyoming meteorologists is that the incoming cold front will be a full-fledged winter weather system and should be treated as such. That means anyone traveling will want to anticipate what they’ll encounter, depending on their timing.
“I do think there's going to be travel problems, especially during the night hours,” Day said. “When it's that cold, the snow accumulates, and ice could accumulate.”
Daytime travel shouldn’t be much of an issue, thanks to the sun angle keeping things just warm and bright enough to melt accumulated ice and snow. According to Day, the biggest “headaches” will be the consistently problematic areas like South Pass, Powder River Pass, Teton Pass, Togwotee Pass, and the section of I-80 between Cheyenne and Rawlins.
“It can freeze and snow during the day, but the April sun is intense enough to get through the clouds,” he said. “The times to watch out for during these April snow events are nights and mornings when it’s dark, and things ice up quickly, and all these areas will be problems overnight on Wednesday, Thursday, and Friday.”
Get It While It's Good
The slow-moving cold front will have moved on by the weekend, and temperatures are expected to moderate to seasonal normals. However, Day said this pattern will set a precedent for the rest of April.
“Next week looks cold and unsettled, with more chances for rain and snow,” he said. “Temperatures over the weekend will still be chilly. It’s not going to stay as cold as it’ll get in Friday, but I expect it to be cooler and unsettled all the way through the end of April.”
According to Day, Wyoming wants it that way. Cooler temperatures will slow the melting of the state’s snowpack, moderating the amount of water flowing into the river basins, fields, and reservoirs.
“You don't want it to be too warm in April,” he said. “Then people start freaking out about the runoff and the mountains accelerating too quickly. You want it more metered and spread out, and this system will slow down the melt in the high country significantly.”
There could be another pendulum swing into the 80s before the end of April, but Day doesn’t think it’s likely. That leaves him with a simple message of calm before the storm.
“Enjoy the next two days,” he said, “because it's going to be a bit before it gets this nice again.”
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
