It gets really hot in summer. On the eastern side of the coastal range, you're looking at 35 celsius during the day. Also lots of forest fires this year (summer 2018). I'm quite jealous, having been to the area, but not ridden it. The scenery, the nature, the rivers, the lakes, are amazing. Hope you like trees and hills!
On the coast it's maybe 20ish and misty quite often. But also beautiful and clean. The sea is too cold to swim. The 101 has quite a bit of traffic.