CHEYENNE – Tuesday’s snowfall – which is one of the earliest on record for Wyoming’s capital city – capped off a recent bout of extreme weather conditions along the Front Range.
Last month, Cheyenne regularly saw high temperatures above 90 degrees Fahrenheit, which helped make history as the hottest summer ever recorded in the area. Over this past weekend, highs remained in the 90s – until the temperatures started plummeting Monday evening.
So what caused these extreme temperature fluctuations?
“The atmosphere is in a constant state of trying to get to equilibrium,” said Bill Mokry, a climatologist at the National Weather Service’s Cheyenne office.
“With the dominant West Coast high pressure systems, we saw those 90- to 100-degree temperatures here on Saturday – and with a couple of storm systems out in the Pacific, the overall atmosphere was very dynamic,” Mokry said.
“With that ridge of high pressure and those warmer airs sitting dominant over the West Coast, it was forcing a lot of these low pressure systems to have to go farther north to get back into the main jet streams. It ended up having to go fairly far north, where it was able to tap into some colder air.”
Although residents of eastern Wyoming and Colorado are no strangers to rapid temperature changes, the dramatic weather conditions seen so far this week are perplexing even the most seasoned weather experts.
“It’s been way more intense and way earlier than we normally see,” said Russ Shumacher, Colorado’s state climatologist and director of the Colorado Climate Center at Colorado State University in Fort Collins.
“That something like this has happened is pretty remarkable, and not something that we have any record of happening before – to go from so hot to snow in such a short period of time,” Schumacher said.
“It will take some research to figure out what the influence of climate change is on a storm like this and all of its different facets. It’s not something we can say right away immediately after it’s happened. But I won’t be surprised if those linkages are made once we get into it.”
Schumacher added that erratic global weather patterns are all interconnected, and that includes the typhoons seen near Asia and in the Pacific last week.
“It really sets up this big rolle- coaster pattern,” he said. “Connecting the pattern in the western U.S. to the pattern that was happening in Asia and the Pacific several days ago, and connecting the dots between all of that will be really fascinating to figure out.”
Tony Bergantino, the interim director of the Wyoming State Climate Office, said it would be difficult to “assign one event in isolation to a particular cause,” such as a warming climate.
He said Tuesday’s snowfall can be attributed to a combination of moisture in the air and the positioning of high and low pressure systems sending the moisture and lower temperatures toward the region.
“What we have is the jet stream being brought far north by a high pressure system south of Alaska. This is bringing the (jet stream) over Alaska before dipping almost straight south and coming down to the west of us, bringing a strong cold front south,” Bergantino said in an email.
“This cold air is moving into a situation where it is going under warmer, moist air, and the low pressure around Utah brings the flow back northeastward over us, where the cold and the combination of moist air is giving us this white blanket.”
Bob Henson, a Boulder-based climatologist and science writer, said the unseasonably cold temperatures, like the kind seen Tuesday in Cheyenne, could potentially be a side effect of an overall warming climate.
“The heat we’ve seen in the West and Southwest this summer has been intense, which is consistent with trends of climate change. As for the rapid swinging – it’s not like we’re seeing a trend toward intense cold in early September – so I wouldn’t call this a climate change trend,” he said.
“But the one way these two things are related is this pile of warm air in the Western U.S. swirling around. ... In a way, it was the atmosphere adjusting to this intense heat dome that brought us this cold air.”
Although the weather events of the past few days have yet to be fully analyzed in a global context, Karen Panter, a horticulturist at the University of Wyoming, said in a news release that the early freeze will damage vegetables and fruits, along with virtually all flowering annuals, both now and into next spring.