It is monsoon season in the desert southwest region of the U.S., which means it is haboob season as well. Haboobs are large dust storms that form in very hot and dry regions when outflow winds from thunderstorms pick up sand of dust and push it across an area. The wall of dust and sand can be very dangerous as visibility can become zero during a haboob.
Phoenix, Arizona usually sees 1-3 haboobs each year, and last night a 3,000 foot tall haboob engulfed portions of the city. Here is a timelapse taken at the Sky Harbor Airport in Phoenix last night.
Check out some more pictures of the dust storm.