...er, uh, well, actually that white stuff coming down from the sky seems to be ash. It's fire season here in Southern California and unusually high winds are whipping up more than a dozen distinct fires into rapidly moving infernos.
We're perfectly safe here in the beach areas (landscape irrigation and concrete are wonderful things), but the ash that's produced by the fires blows over here and falls from the sky like snow (except warm, dry, and stinky).
The good news is that last time this happened, my rose bushes bloomed really well for a couple of years. They must've liked the ash.