The National Weather Service issued a blowing dust advisory for southeastern Arizona on Tuesday from 2pm to 8pm local time, warning that thunderstorms could suddenly cut visibility to near zero and stir up fungal spores capable of causing the potentially fatal lung disease Valley fever.
The agency urged residents with respiratory problems to stay indoors until the storm passed and told drivers to pull off the road if they encountered a wall of dust.
The alert came amid warnings that so-called "fungal storms" could threaten communities across at least 11 states throughout the summer.
Dust storms can disturb soil containing Coccidioides, a microscopic fungus responsible for Valley fever, and carry its spores through the air. Arizona officials had not confirmed that Tuesday's dust contained the fungus, but the storm was developing in a region where Coccidioides is found.
Experts fear the threat will intensify as the Southwest moves deeper into the North American monsoon season, when thunderstorms and powerful winds whip up enormous walls of desert soil.
What the weather service warned
The National Weather Service said dust would reduce visibility to between one-quarter and one mile shortly after the storm developed after 2pm, with wind gusts expected to exceed 40mph. Local meteorologists said winds could reach 60mph.
"If you encounter blowing dust or blowing sand on the roadway or see it approaching, pull off the road as far as possible and put your vehicle in park," the agency said. "Turn the lights all the way off and keep your foot off the brake pedal. Remember, 'Pull Aside, Stay.'"
The advisory covers a large swath of southeastern Arizona, including eastern Cochise County, the Upper Gila and San Pedro River valleys, and the Chiricahua, Dragoon, Mule, Huachuca, Santa Rita, Galiuro and Pinaleño Mountains.
Monday's storm near Phoenix
A violent dust storm hit outside Phoenix on Monday evening, stretching as far as Tucson, more than 100 miles south.
Meteorologist Jorge Torres said Monday night's dust storm was still lingering over the Valley on Tuesday morning, with air quality readings ranging from unhealthy to hazardous. He said sensitive groups should limit their time outdoors early in the day.
What causes Valley fever
Coccidioides grows naturally in dry, sandy soils in certain arid parts of the world, including the U.S. Southwest. It thrives in alkaline-rich soils with hot summers, mild winters and low rainfall, and is generally harmless to most people unless it is blown into the air and inhaled into the lungs.
Most people infected with Valley fever suffer flu-like symptoms, but in severe cases the fungus can spread beyond the lungs to the bones, brain and other organs, potentially becoming fatal. The Centers for Disease Control and Prevention has called the infections rare, though it has acknowledged that some outbreaks have happened in places where scientists did not expect the fungus to live.
Cases climbing across Arizona
Valley fever cases have continued to climb across Arizona, with Maricopa County alone recording 4,498 infections during the first six months of 2026.
More than 12,000 cases were reported statewide last year, and Arizona typically accounts for roughly two-thirds of all U.S. infections.
Researchers have found that Valley fever cases have risen dramatically in recent years across the Southwest, though experts are not sure exactly what is driving the increase.
Infections surged across the Phoenix area in 2024, climbing 42 percent to 12,522 cases from 8,841 the previous year, according to state health data. The increase was reflected nationwide, where the annual case count jumped from 16,746 to 22,244.
