At least five die after storm causes Montana highway pileup

Traffic is backed up on Interstate 90 after a fatal pileup where at least 20 vehicles crashed. Photo / AP

At least five people have died after a dust storm fuelled by wind gusts topping 97km/h caused a pileup on Interstate 90 in Montana, authorities said.

More than 20 vehicles crashed and Montana Highway Patrol Sergeant Jay Nelson said authorities believe the weather was the cause.

"It appears as though there were heavy winds, causing a dust storm with zero visibility."

While the highway patrol did not have an immediate count of the number of injuries, Nelson said additional ambulances had to be called in from Billings to help.

Governor Greg Gianforte said on Twitter: "I'm deeply saddened by the news of a mass casualty crash near Hardin. Please join me in prayer to lift up the victims and their loved ones. We're grateful to our first responders for their service."

I'm deeply saddened by the news of a mass casualty crash near Hardin. Please join me in prayer to lift up the victims and their loved ones. We're grateful to our first responders for their service.

— Governor Greg Gianforte (@GovGianforte) July 16, 2022

The incident happened 5km west of Hardin.

But the dust storm's roots can be traced back several hours, when storms popped up in central southern Montana between 1pm and 2pm and slowly began moving east, according to Nick Vertz, a National Weather Service meteorologist in Billings.

A so-called "outflow" — or a surge of wind that's produced by storms but can travel faster than them — flew east/southeast about 48km ahead of the storms, Vertz said.

A 64km/h gust of wind was recorded at the nearby Big Horn County Airport at 4.15pm. The crash was reported to the highway patrol at 4.28pm.

First responders work the scene on Interstate 90 after a fatal pileup where at least 20 vehicles crashed. Photo / AP

By the airport weather station's next reading at 4.35pm, the gusts had picked up to 100km/h. Another reading 20 minutes later recorded a gust of 103km/h.

The wind easily picked up dust — a product of recent temperatures into the 90s and triple digits over the last week — and reduced visibility to less than 0.4km.

"If they looked up in the sky while they're in Hardin, they probably didn't see much of what you'd think of for a thunderstorm cloud, maybe not even much at all," Vertz said.

"It was just a surge of wind that kind of appeared out of nowhere."

As first responders attempt to clear the wreckage, the meteorologist said they can expect to be safe from additional winds and thunderstorm activity.

"It should be a relatively clear, calm night for them."