Haboobs are rolling dust and sand clouds formed by collapsing thunderstorms. When thunderstorms collapse winds rush to the surface and spread out along the ground. The strongest winds spread in the direction that the thunderstorm is moving. The southwest has been very dry lately so this collapsing thunderstorm had alot of loose dust and sand to work with as it formed a dust and sand cloud some 5000 feet high and up to 100 miles long. The haboob was moving at some 50mph and created visibilities near zero.