Pictures: Huge Dust Storm Swallows Phoenix

PHOENIX -- Metropolitan Phoenix was shaking itself off Friday after a giant wall of dust smacked the city for the third time in the last six weeks, turning the skies brown and coating anything left outside. A 1,000-foot-high wall of dust traveled at least 50 miles into metro Phoenix and neighboring Pinal County on Thursday evening before dissipating. It reduced visibility, created dangerous driving conditions and caused some flight delays. National Weather Service meteorologist Ken Waters said the size and power of three of the storms set this season apart. Thunderstorms moving through southern Arizona brought winds of up to 60 m.p.h. that stirred up fine dust in the agricultural fields, Waters said. This season's most powerful dust storm came July 5, when a mile-high wall of dust halted flights and knocked out power to 10,000 people. Another dust storm hit July 18, reaching heights of 3,000-4,000 feet, delaying flights and cutting power to more than 2,000 people. 

Weather experts said such massive dust storms -- known by the Arabic word "haboob" -- happen in only Arizona, Africa's Sahara desert and parts of the Middle East. They cause pollution levels to skyrocket and can create health issues. Dennis Dickerson, a compliance manager at the Maricopa County Air Quality Department, said the normal level of dust in the air is 20-70 micrograms per cubic meter. Thursday's 24-hour average for Phoenix reached nearly 160 -- slightly above what federal standards deem healthy. Dr. Art Mollen of Scottsdale, Ariz., said there were twice as many patients as usual in his waiting room at the start of work Friday. People came in with asthma flare-ups, sinus inflammation, ophthalmological migraines and other problems.