Wind blow dish down, go boom.
Apparently we didn't tighten the bolts enough, and last night we had our first rain of the season. "What do we need lightning arrestors for?" we said. "When's the last time you saw lightning in San Francisco?"
So, we waited until this afternoon to send Bishop down the pipe to re-align the dish, since he didn't want to brave the roof in 70+MPH winds last night. Sissy.