That's because the local boosters down there didn't want to scare off
the folks moving in from Kansas back during the boom years, so the
local media called them "Microbursts". There's a chapter on this in
_Ecology of Fear_ by Mike Davis, an L.A. area writer.
That is a first in California I think.
As I remember the book, it's more like two a year in the L.A. area.
Interesting things happen when the local newspaper company is also
a big real estate developer.