The Greater Phoenix area was treated to a rush hour sand storm that completely covered the city, knocked out power to 12,000 residents, and delayed flights on Friday. They call the sand storm a "haboob" from the Arabic word.

From the Christian Science Monitor

The dust storm cut visibility on the roads, with reports ranging from no visibility to 1/2 mile just south of the Valley before the storm hit the Phoenix area.

Ahead of the storm, a "blowing dust advisory" was issued by the National Weather Service, warning of rapidly dropping visibility and "thunderstorm outflow winds of 25 to 40 mph."

According to CSM, the dust storms are caused by down drafts, which happen as a result of powerful thunderstorms that spread across the Southwest during its monsoon season. Here's what it looked like: