The Southwestern US has dramatic cloudbursts; what makes some of them so localized?

Question

For instance, a very clear blue sky with one smallish cloud dumping a torrent of rain, but otherwise nice weather. If the cloud comes near, you step under shelter for a minute and wait for it to pass. Quite remarkable, I'd say. Seems almost surreal. How could one little cloud dump so much water and not 'fizzle out' ?

Answer 1

Southwestern thunderstorms do fizzle out quickly, at least compared with midwestern supercells.  Often in the southwest the thunderstorms will form over the high elevation areas, where there is enough upward motion to make them, then move out into the surrounding terrain.