Every year is alittle different. San Francisco can be quite foogy this time of year. Plan on it being fairly cool. June will probably be more so than May. I still can't believe how much we freeze in August when we go!
Yosemite will be balmy weather, most likely, but cools down incredibly quickly as the sun sets. That's the mountains for you.
Southern Cal...usually beautiful this time of year. Not too hot yet, Santa Ana winds usually don't kick up til later in the summer, as I recall, and the fog isn't usually a problem either.
That being said...this year has been odd. Tahoe is getting snow in its highest peaks. But earlier in the week we were seeing record highs.
Keep a close eye on the weather reports right before you leave and go with it, but plan on some cool weather JUST IN CASE.