What's the etiquette here? (Workplace Edition)

As some of you know, my girlfriend moved out and away a few weeks ago because she got a job in California.

For various reasons I chose to stay back at the homestead in Missouri for a few more months, but I'm planning to join her in the Bay Area in early summer.

Of course that means I'm going to quit my job in a few months, and I guess I'm feeling kind of weird about that? Yeah, I'm feeling kind weird about it because I know I'm going to leave my work in a few months, but my employers don't. Am I supposed to tell them now, or do I just turn in a standard two-week notice (as is my current plan)? This isn't the first job I've quit, but I don't think I've ever known my exit strategy this far in advance. I'm just worried that if I tell my bosses now, they'll get super pissed and fire me immediately. (I don't know if that's a thing that happens or just a product of my severe anxiety-riddled brain.) For what it's worth, when I was hired I think it was understood that I wouldn't be at the station for more than a year or two because most people, especially non-natives like me, don't ever last at the station for too long.

Okay, that's enough rambling. TL;DR: how soon should I tell my supervisors that I'm leaving my job this summer?