A Monday afternoon thunderstorm literally blew through Thermopolis, creating a surge of strong winds downtown and sparking several fires in the region.
Thermopolis Volunteer Fire Department Chief Mark Collins told Cowboy State Daily that the agency responded to two active fires in “the Warm Springs area” east of town. One fire was estimated to be around 500 acres, while the other was around 150 acres.
“We think the two fires are going to burn together,” he said. “Some oil field structures may be in danger at this time, but we’re monitoring the situation and seeing how the fires burn.”
They fires were 0% contained, and Collins said he’s notified the Bureau of Land Management Cody Dispatch to coordinate a response.
Suddenly, Wind
Jessica Lippincott was traveling down Broadway Avenue when she saw the sudden windstorm move toward downtown Thermopolis. It was generated by a small thunderstorm that formed over Hot Springs County in the afternoon.
“I saw it coming in from the south,” she said. “Then it hit Broadway and just went straight down downtown.”
The sudden surge sent an American Flag spinning as the pole carrying it was bending with the force of the wind. Debris from streetside storefronts was blown across the street and into the air, and one store lost a section of its roof.
It was wet and furiously windy in downtown Thermopolis for less than 20 seconds before the winds stopped. Meanwhile, nearby, lightning strikes from the same thunderstorm sparked fires in the nearby hills.
“I saw the smoke coming about two miles east of the north side of the Wind River Canyon,” said Michael Stevens, who saw the smoke from the Tipi Retreat Ranch.
Summer Winds Coming Blowing In
Cowboy State Daily meteorologist Don Day said the winds observed in Thermopolis were “classic outflow winds” from late afternoon thunderstorms. The winds generated from these severe, but isolated, thunderstorms come from the descent of cool air in arid conditions.
“When the rain from those clouds hits drier air closer to the ground, it evaporates before it gets to the ground,” he said. “The evaporation process creates a cool pocket of air below the base of the cloud, and since the air is colder, it's denser. Then gravity takes over, forcing the dense air to the ground.”
Incredible winds are created when gravity compresses the cooler, denser air as it reaches the ground. Day compared it to putting a thumb over the end of a garden hose, which increases the pressure and speed of the flowing water.
Wind gusts generated by the compressed air can get as high as 60 mph. Day wasn’t aware of any recorded wind speeds in Thermopolis that afternoon, but the videos of the scene gave an idea of how intense it got downtown.
“The only thing I could do was look at that flag, which looks like it’s in the 40-50 mph range,” he said.
Started It, Won’t Finish It
Day said several isolated thunderstorms moved across Thermopolis on Monday, generating the nearby fires. While these furious outflow winds can happen in the wake of any thunderstorm, Thermopolis’s terrain tends to amplify the impact.
“If you think about the terrain around Thermopolis, it’s rugged all around, and you've got the Wind River Canyon right there,” he said. “That just exacerbates it. When you put these gusts of winds through complex terrain, that squeezes it even more, makes it more turbulent, and can cause a lot of havoc in a short period of time.”
Unfortunately, the thunderstorms that generated the lightning-strikes fire didn’t carry enough moisture to extinguish them. According to Day, it’s another hazard of late-summer thunderstorms where it’s cool enough to generate moisture but dry enough to prevent it from reaching the ground.
“Small late-summer thunderstorms lend themselves to generating lightning without a lot of rain, so the rain doesn't put out the fire,” he said. “That's a problem this time of year.”
Contact Andrew Rossi at arossi@cowboystatedaily.com
Andrew Rossi can be reached at arossi@cowboystatedaily.com.
