Actually, it wouldn't have the slightest effect on San Francisco. The wind essentially never, ever blows east to west there.
Check out my post 68. The whole U.S. was affected by the yellowstone event. Kinda blows a hole in your west to east theory.
Yeah, the Easterners will die in a few hours to weeks from suffocation and lung infections. Westerners will riot & finally starve to death over the course of months and years.
In an eruption of the size contemplated (i.e. HUGH), the winds won't be what you would expect, and there is no way that normal winds (and you are really only thinking of sea-level winds) could keep all that ash to the east of the eruption.
No offense, but you are just wrong on this one.