An ominous wall of dust spanning 70 miles and reaching 5,000 feet tall engulfed the Phoenix area Thursday in the Valley’s latest eye-popping, tree-toppling monsoon storm.

The severe dust storm with winds that ripped through the West Valley at 70 mph was the largest to hit Arizona so far this year, said Larry Hopper, a meteorologist for the National Weather Service.

The storm uprooted trees, downed power lines and damaged homes. But it’s not the biggest wall of dust to ever hit the Phoenix metro. 

That record was set seven years ago, one day after the Fourth of July.

On July 5, 2011, a mammoth plume of dust 8,000 feet high and 200 miles wide blanketed the city.

The striking weather spectacle blackens desert skies, drawing comparisons to the eerie storms from science-fiction writer Ray Bradbury’s “Something Wicked This Way Comes.”

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On Thursday, the National Weather Service Phoenix warned people of “dangerous life-threatening travel” and “near-zero visibility in blowing dust.”

People on social media posted photos of giant-dust clouds that looked like smoke rising after a bomb. Some weather buffs took to Twitter and Facebook to talk about the science behind the storms.

How do dust storms form?

Dust storms form when dry air accumulates between the base of a cloud and the ground surface, Hopper said.

In Arizona’s deserts where it is especially warm and dry, these formations of dust are common.

“The magnitude depends on how strong the (wind) gusts are,” Hopper said.

The southwest and southeast parts of the state, specifically near Tucson, are prone to dust storms due to their desert terrain. Hopper said dust will often accumulate in that region in the early afternoon before traveling to the Phoenix area at about 5 or 6 p.m. when the number of drivers on the streets and freeways spikes.

Are there signs a dust storm is coming?

Hooper said very dry conditions are often the clearest indicator that a dust storm is on the horizon, which is why many such storms blow through the Valley at the beginning of monsoon season.

However, further into Phoenix summers, thunderstorms can also foreshadow potential blowing dust.

When a thunderstorm collapses on the ground, it produces outflow, or winds from the collapse, that can kick up heavy amounts of dust.

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What kind of damage can the storms cause?

While a dust storm looks scary and destructive as it starts to move through the Phoenix area, Hopper said it is often the 60 to 70 mph winds that accompany the storms that create dangerous weather conditions.

“Winds themselves can do damage,” Hopper said. Dust causes “hazards driving on the roadways,” he said.

The Arizona Department of Transportation uses the motto “Pull Aside, Stay Alive” to warn people not to drive in a dust storm. 

The most important tips, according to ADOT, are to avoid driving directly into the storm, try to exit the highway if possible, turn off all vehicle lights and use the emergency brake.

Safety guidelines can be found at pullasidestayalive.org.

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