The dust storms in Arizona are an interesting phenomenon because of their scope. The storms are caused by winds which may be blowing in a storm front or monsoon and a heavy rain shower usually follows a large dust storm. The largest storms can build clouds of dust that can engulf even the largest buildings and these clouds usually sweep over downtown Phoenix. I would estimate that the storms can be as tall as sixty stories. The visual effect is quite stunning; the cloud itself is almost totally opaque, so it appears as if entire buildings and city blocks are being swallowed in a redish brown blob. This was particularly striking in 1999, when Doomsday Hysteria was at a fever pitch.