Winter thunderstorms aren’t uncommon in Wyoming in April and May, but they shouldn't be underestimated. They can quickly turn a placid day into blizzard conditions with heavy snow, lightning and thunder.
Several short, but severe, winter thunderstorms contributed to the chaos that unfolded across Interstate 80 on Thursday and Friday. When the latest winter weather system caused several winter thunderstorms to form, creating hazardous driving conditions that forced most of I-80 to shut down.
“These thunderstorms dissipate quickly, but in that time, they unleash,” said Cowboy State Daily meteorologist Don Day. “We can get intense snowfall in a relatively small area in less than 30 minutes. If that storm occurs over a town or highway, it causes problems like we saw on I-80.”
There's still a wide window of opportunity for winter thunderstorms to form and create chaos over the next month. Spring may have sprung, but that doesn't mean Wyoming's winter is over.
The Thunder Of Winter In Spring
The ingredients for thunderstorms are the same, no matter the season, Day said. All that’s needed is warm, moist air lower in the atmosphere that gets forced up and over cold air aloft.
Thunderstorms are rare between November and February because the air is predominantly cold with few influxes of the warm, moist air needed for the mixture that leads to thunderstorms. But during spring, warm spells are often followed by cold fronts, which are the conditions that can lead to the formation of multiple winter thunderstorms.
Just like their summer counterparts, winter thunderstorms drop a lot of precipitation in a short amount of time. When it’s cold enough for the rain to turn into snow, it falls and accumulates faster than it can melt.
“It comes down so fast that it doesn’t matter if the ground is warm — it’s going to accumulate,” Day said. “That’s one reason why these spring storms can be such a problem.”
Lightning generated by winter thunderstorms creates its own hazards. In an already dry environment, the snow of a winter thunderstorm could (theoretically) extinguish a wildfire that was started by lightning from the same storm.
“Theoretically, it could happen,” Day said.
Summer thunderstorms tend to cover vast areas. Winter thunderstorms are more condensed, but that doesn’t reduce their severity.
Instead of one singular storm, a cold weather system can cause multiple small thunderstorms to form across its front. This creates waves of severe winter weather with varying intensity.
Day said the weather conditions in southern Wyoming on Thursday were ideal for creating several winter thunderstorms that led to intense snowfall. When the cold front arrived, temperatures were still relatively mild, in the 40s and 50s, particularly between Laramie and Wamsutter.
“As the cold front arrived, the thunderstorms formed,” he said. “Most of them started as rain, but as they grew and got colder, there was a quick changeover to snow. That’s what caused all the issues on I-80 yesterday.”
Highway To Heaven (Or Hell)
The stretch of I-80 between Evanston and Lyman is sometimes called the “Highway to Heaven” because of an optical illusion that appears to make the pavement stretch into the sky. During spring storms like the one Thursday, the entirety of I-80 in Wyoming quickly turns into a highway from hell.
I-80 is always prone to high-impact winter weather because it is so close to heaven. Day said the high elevation exacerbates the severity of any winter weather system that reaches the interstate.
“The elevation around Elk Mountain is well over 8,000 feet, and then you’re between 6,000 and 7,000 feet all the way from the Continental Divide to the Red Desert,” Day said. “It's so high in altitude that it’s more common to get snow rather than rain at this time of year, and we saw multiple thunderstorms crisscross the I-80 corridor at its highest points on Thursday.”
Day was still waiting for Thursday’s snow totals, but the numbers he’d seen already demonstrated the severity of the snowfall caused by winter thunderstorms. I-80 might be prone for more of these short and severe storms, but they can happen anywhere in Wyoming with the right conditions.
“I've seen liquid amounts between a half inch and an inch between Elk Mountain and Wamsutter,” he said. “That’s roughly 5-10 inches of snow, maybe more. Lander got over an inch of water during this storm.”
That’s a lot of snowfall for any winter storm. Now, imagine that much snow falling over a small area in less than 30 minutes — that’s the reality of winter thunderstorms.
Most of Wyoming will gladly welcome this moisture, but winter thunderstorms force it to fall faster and heavier than drivers might anticipate.
“When seasons change, you have the right ingredients for these spring storms to have thunderstorms embedded in them,” Day said. “Thursday was a ripe environment for thunderstorms. The moisture is a real shot in the arm, but this is how we tend to get it at this time of year.”
Moderating Back To Mild
The outlook for next month shows a good chance that similar winter storm systems could move across Wyoming. This means more chances of winter thunderstorms manifesting as these systems move south.
“Next week is going to be very spring-like,” Day said. “We'll get back to mild temperatures, but we'll also have chances of afternoon showers and thunderstorms. So there's a good chance that parts of Wyoming will experience thunder between Monday and Friday next week.:
It’s too early to determine whether those thunderstorms will bring rain or snow can’t be determined yet, but the chances are still somewhat high. Day’s oft-stated truism is that Wyoming can’t say goodbye to winter until after Mother’s Day – that leaves 22 days where the winds of winter could still blow.
“I think there are at least two more chances we’ll get snowed on again between now and Mother's Day weekend,” he said. “Last Friday, I got my grill, cooked a couple of steaks, and had dinner outside. That's not likely for this or next Friday.”
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
