Towering dust storm known as a haboob plunges Phoenix into darkness

A massive dust storm swept through Phoenix and other parts of Arizona on Monday, casting an apocalyptic pall over the region as the towering wall sank the city into darkness and caused heavy rain and lightning.

The haboob – an intense, fast-moving wall of dust kicked up by thunderstorm winds – hit the state during the evening commute. The National Weather Service urged drivers to “pull aside stay alive” as visibility shrank to as short as 50 feet.

The haboob was the result of a thunderstorm complex that developed north of Tucson, Arizona, in the Santa Catalina Mountains. Cool air exhaust fanning outward ahead of the storm – called outflow – picked up large amounts of sand as it moved across the desert near Cactus Forest, along Highway 79.

Between 5:35 p.m. and 5:51 p.m. local time, Phoenix Sky Harbor International Airport reported a visibility of zero miles. The automated sensors used by the National Weather Service report visibilities in increments of 1/16 of a mile, which is roughly the length of a city block. For a sensor to round down to zero means actual visibility was less than half that, or below 165 feet.

In some cases, drivers could barely see beyond the hood of their cars.

Pushing north, the plume reached Phoenix, where Sky Harbor International Airport recorded a wind gust of 70 mph just before 6 p.m. as the haboob moved through. San Tan Valley, on the southeastern fringe of the Phoenix metro area, gusted to 94 mph. Chandler Municipal Airport gusted to 67 mph, and Mesa’s Falcon Field to 66 mph.

The haboob and the deluge that followed caused flight delays at Sky Harbor and widespread power outages, downing trees and utility poles. Police in Gilbert, just southeast of Phoenix, said the storms knocked out some traffic lights.

The National Weather Service issued flash flood warnings as water overtook a portion of southbound Interstate 17, forcing closures. The airport in Phoenix picked up 0.28 inches of rain, but other parts of the city saw up to an inch.

Haboobs are common in arid regions like the Desert Southwest and the Middle East, where the term originated. They tend to strike in the Southwest during the North American monsoon season, which comes around July and August.

A monsoon is a seasonal wind shift. During the summer months, southerly winds pump north moisture from both the Pacific Ocean and western Gulf. That moisture helps isolated, slow-moving thunderstorms blossom. About 30 percent to 50 percent of annual rainfall in Arizona and New Mexico comes from the monsoon; for western Mexico, especially in Sonora and Sinaloa, it’s more than 80 percent.

The biggest hazard with haboobs is the low visibility, particularly for motorists. Guidance from the National Weather Service urges motorists to avoid entering a dust storm and, if not possible, to pull off the pavement, set the emergency brake, fasten seat belts and turn off lights. (Approaching drivers have been known to accidentally hit parked vehicles while using their lights as a guide for staying on the road.)

When the National Weather Service issues a dust storm warning, cell carriers send wireless emergency alerts – those notifications that make your cellphone blare – to alert drivers and spur them to pull over.

Monday’s haboob came after a weekend dust storm overtook the annual Burning Man festival in Nevada, more than 600 miles northwest of Phoenix. Not all dust storms are considered haboobs, which can stretch for dozens of miles and rise thousands of feet.

Additional widely scattered thunderstorms are possible Tuesday as continued monsoonal moisture festers over California, the Intermountain West and Desert Southwest.