In fact, they're really not for rain at all considering it never rains. Seriously...NEVER. Or basically never. Which is weird considering that when we were kids it used to rain so hard that it would flood and we would go swim in the streets.
Nowadays, umbrellas in Vegas are mostly a small respite from the scorching, intense sun and the sweltering, unrelenting heat that accompany it. Everyday that I drive around town, I see people walking down the sidewalks with umbrellas over their heads.