Dust storms that blanketed the Phoenix area in thick haze this week were among the most intense to hit the region in years, scientists said Thursday.
The storms — called haboobs — occur throughout the U.S. Southwest when strong downdrafts from thunderstorms stir up loose dust and dirt that get blown along in front of the approaching storm cell.
They can produce massive walls of dust and debris that blind drivers and make people sick.
The latest storm rolled in during the early morning hours Thursday, three days after the other one struck. There were no reports of any significant impacts, though both storms reduced visibility to half a mile (0.8 kilometers).
“Luckily, they both happened when it was later at night, so there was less traffic on the roads,” said National Weather Service meteorologist Matt Salerno in Phoenix.
Both storms were extreme, Category 5 events on a scale of dust storm severity, with huge concentrations of dust and wind speeds of about 50 mph, according to researchers at Arizona State University, which helped develop the scale.
The scale — unveiled this year — was developed using data going back to 2010.
“To have Class 5 dust storms occur one right after another a few days apart is unprecedented in our records,” said Randall Cerveny, a professor in the School of Geographical Sciences and Urban Planning at Arizona State. “We don’t see that.”
They were only the fifth and sixth dust storms in the last 16 years to reach Category 5, Cerveny told The Associated Press in a phone interview.
He noted the Phoenix region has been drier than normal, which can increase the amount of dust that is kicked up. Scientists have said human-caused climate change increases the odds of both severe drought and heavier storms that could set the stage for more intense dust storms in the future.