[barathr]

I've grown and grafted Avocado trees in both Northern and Southern California. Hass, Reed, and many other good types will fruit well in Redwood City and virtually all of the Bay Area.

The only areas that can't grow Avocados are the Sierras. It's even possible to grow them in Humboldt:

https://www.epicenteravocados.com/varieties/version-2-2/

[throwup238]

What time do they start showing flowers? I want to plant a few here in SoCal but I'm at around 3k elevation and we get an annual March snowstorm that likes to kill off any plant that start to show early.

[barathr]

They usually flower in Spring, whenever that is for you. It's cultivar and temperature dependent. Some varieties like Carmen will even flower multiple times a year (though Carmen isn't one of the more cold hardy types). Bonny Doon is a good cultivar to consider if you get some mild frost each year. If you go below 20 degrees, though, you'd need to protect the tree during the cold snap.