A massive dust storm, called a haboob by meteorologists, swept across central Arizona in late August. In the city of Phoenix, officials were forced to briefly ground flights, and tens of thousands of people lost power. Dust storms such as these form when powerful winds from thunderstorms lift large amounts of dust and debris into the air. The haboobs can stretch for miles, rise thousands of feet into the sky, and arrive with little warning, causing sudden and severe decreases in visibility. They may also stir up pollutants and infectious spores that could cause respiratory illnesses, so experts recommend staying inside until the air clears. Although dust storms are common in the desert zones of the Southwestern United States during heavy rains, this one stood out for its size, with forecasters estimating the dust cloud was 6,000 to 8,000 feet tall, or about as tall as five Empire State Buildings. “In the seven years that I’ve been here, it was the biggest that I’ve seen,” says Sean Benedict, a meteorologist with the National Weather Service in Tempe.