Extreme Wyoming Weather Swings From 10 Inches Of Snow To 90 Degrees In A Week

Last week, parts of Wyoming got up to 10 inches of snow during blizzard conditions. By Monday, temperatures were in the 80s and flirting with record highs—on their way into the 90s by Wednesday. While Wyomingites may wonder why the state’s climate suddenly has the temperament of a moody teenager, meteorologists say the state has always been subjected to “roller coaster” weather in May.

Cowboy State Daily meteorologist Don Day said these week-to-week changes are part of what he affectionately calls “Moody May.” “May is very susceptible to mood swings,” Day said. “In less than a week, we’ve had a snowstorm, funnel clouds, severe thunderstorm warnings, and record-breaking high temperatures.”

Less than a week ago, Cheyenne received an inch of liquid water from rain and snow, with temperatures statewide dropping into the 30s and 40s. On Monday, Cheyenne’s daytime high was 82 degrees. Meteorologist Adam Dziewaltowski with the National Weather Service office in Riverton said Lander’s record high for May 11 was 84 degrees, set in 1940; Monday’s forecast was 85 degrees. Casper’s record of 83 degrees, also set in 1940, was expected to be broken with a high of 84.

This is the beginning of a warm wave that will cover Wyoming this week, peaking Wednesday. “Places like the Bighorn Basin could get into the mid-90s on Wednesday,” Dziewaltowski said. “Those temperatures could be flirting with monthly high-temperature records.” He added that while extreme swings can happen this time of year, “what’s unusual is that it’s a lot warmer earlier than we expected.”

“Like a teenager, May is moody,” Day said. “When you get into this time of year, you have these battles of air masses. Last week, Canada won. This week, the deserts won. That’s how you expect the pendulum to go back and forth as the seasons are trying to change.”

Both meteorologists said Wyoming is not “locked into” an extended period of warm, dry weather. After reaching or exceeding 90 degrees by Wednesday, the extended forecast anticipates daytime highs in the high 50s to mid-60s by Sunday, with a slight chance of rain and snow showers in some spots. “We have a pretty big warmup this week, followed by a big wave of cooler air coming in behind it by the weekend,” Dziewaltowski said. “It’s not out of the ordinary to go from cold temperatures and snow to hot, dry weather. I’d say that’s the Wyoming norm.”

Day is not extending his forecast far beyond the weekend. Some weather outlets have called for a snowstorm along the Wyoming-Montana state line, with some models showing as much as 10 inches in Johnson County. “I’m not going to start throwing out inches that far in advance,” Day said. “Trend is your friend. I’ve got some models that definitely show colder, wet weather statewide on Sunday, and some models that don’t show that at all. I would say the trend is that the latter half of the weekend and early next week is colder.”

Dziewaltowski reassured Wyomingites that nothing is stuck in place. “There’s no indication that we’re locked into hot, dry weather,” he said. “Conditions are more volatile. We’re looking at more up-and-down swings over the next two weeks, and that’s normal for these transition seasons.”