Haboobs are dense, atmospheric walls of dust or sand that are encountered in arid regions across the globe. Ironically, they usually develop during the monsoon season when downdrafts from nearby thunderstorms produce outflow gust fronts that sweep particulates into the air. Moving out from the central storm, the imposing wall may be a mile or more high and closes in at 30-50 miles per hour, producing a visual doomsday effect.
Though short-lived, haboobs dramatically reduce visibility and, while they may bring destructive winds and induce breathing difficulty, their primary danger results from the rapid loss of visibility, leading to vehicular accidents. Fortunately, they can usually be spotted from a safe distance and modern radar systems provide ample warning of their development, reducing the occurrence of injuries and fatalities.
Yesterday's haboob in Phoenix, Arizona, was spawned by a cluster of thunderstorms northwest of Tucson. According to the Weather Service, this arc of dust and sand was 60 miles across, one of the more spectacular haboobs to strike the Desert Southwest in recent years.