The weather phenomenon behind deadly crash on I-15

I-15 Dust Storm
Posted at 10:21 PM, Jul 25, 2021
and last updated 2021-07-26 14:55:36-04

SALT LAKE CITY — What appeared to be a sand or dust storm is behind one of the deadliest days ever on a Utah highway, with at least seven fatalities Sunday coming on a stretch of Interstate 15 in Millard County.

Photos and video taken ahead of and during the incidents showed heavy clouds of dust quickly blowing across the highway as drivers moved through the area.

But while the simple answer is to explain the weather phenomenon as a sand or dust storm, and there are differences, the reality is more complicated. Both are characterized by strong winds, although since sand is a much larger particle than dust, it does not travel as far, as high or for as long as dust.

FOX 13 meteorologist Brek Bolton spoke with the National Weather Service office in Salt Lake City who said the storm that ran ahead of the accidents was a "microscale" event associated with nearby thunderstorms. The NWS told Bolton that a sensor reported a 32 mph wind gust close by, and that speeds may have been stronger in the area of the highway.

Thunderstorms produce strong gusts with outflow with a downward draft, which are enhanced with nearby mountain slopes, said Bolton. Those gusts kick up the dust and send them flying across the landscape.

AccuWeather reports dust storms, which are more widespread that sand storms, can cause the blinding conditions that appeared Sunday in Millard County. They warn drivers to pull off the side of the road and get as far away from travel lanes as possible should a dust storm appear.