A launch from Vandenberg, seen from San Francisco
From San Francisco, Vandenberg SFB is about 376 km away to the SSE (compass bearing 153°). A night or twilight launch is likely visible; a daytime launch is unlikely to see. Face SSE shortly after liftoff and watch low on the horizon — the rocket climbs as it heads downrange.
You're not watching the rocket itself — beyond a few km the vehicle is far too small to see. What's visible is the engine plume at 65–100+ km altitude: at night a brilliant moving flame (routinely seen 300+ km away), at dawn/dusk a sunlit "jellyfish" cloud that has been documented 800+ km away, in daytime only a white contrail with much shorter range. Cloud cover, local horizon and trajectory all matter.
Nearby cities
For exact launch times and live trajectories, check the provider's stream. How this estimate works.