Twenty-one vehicles crashed and Montana Highway Patrol Sgt. Jay Nelson said authorities believe weather was the cause.
“It looks like there were strong winds that caused a dust storm with no visibility,” he said.
While highway patrol couldn’t immediately count the number of people injured, Nelson said additional ambulances would have to be called from Billings to help.
Gov. Greg Gianforte said on Twitter: “I am deeply saddened by the news of a mass casualty accident near Hardin. Please join me in prayer to lift up the victims and their families. We are grateful to our first responders for their service.”
Montana Attorney General Austin Knudsen, who oversees the Highway Patrol, said in a statement, “The Montana Highway Patrol is on the scene with other first responders investigating the incident. We will release more information as it becomes available and appropriate out of respect for the lives lost and their loved ones.
“My prayers are with everyone affected by the tragic events of the dust storm in Big Horn County today,” Knudsen added.
The incident happened 5 kilometers west of Hardin. Video from The Billings Gazette showed hundreds of semi-trucks, RVs and cars stuck in traffic for miles along the eastbound two lanes of the Interstate.
The dust storm’s roots can be traced back several hours, as storms emerged between 1 p.m. and 2 p.m. in south-central Montana, slowly moving east, according to Nick Vertz, a meteorologist with the National Weather Service in Billings.
These storms triggered a severe thunderstorm watch that covered Hardin and other parts of Montana from afternoon through 9 p.m. Friday. Meteorologists forecast the potential for isolated quarter-size hail, isolated wind gusts of up to 75 mph (121 km/h) and frequent lightning.
A so-called “outflow” — or wind wave produced by storms but faster than it can travel — flew east/southeast about 30 miles (48 kilometers) ahead of the storms, Vertz said.
A 40 mph (64 km/h) gust of wind was recorded at nearby Big Horn County Airport at 4:15 p.m. The accident was reported to the Autobahn Police at 4:28 p.m
When the airport weather station measured the next time at 4:35 p.m., the gusts had increased to 100 km/h. Another measurement 20 minutes later showed a gust of 64 mph (103 km/h).
The wind slightly picked up dust – a product of recent temperatures well into the 90s and in the triple digits over the past week – and reduced visibility to less than 1/4 mile (0.4 km).
“If you’ve been looking up at the sky while you’re in Hardin, you probably haven’t seen much of what you would think of as a thundercloud, maybe not at all,” Vertz said. “It was just a gust of wind that came out of nowhere.”
As first responders attempt to clear the wreck, the weather forecaster said they can expect to be safe from additional winds and thunderstorm activity.
“It should be a relatively clear, calm night for them,” he said.
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https://abc13.com/montana-deadly-storm-highway-pileup-6-dead/12055546/ Deadly storm: Six people were killed in a pile-up on Interstate 90 in Montana on Friday night.