I also expect that you will be riding north-to-south - with the ocean to your side and with a tailwind.
The Pacific Northwest climate pattern is one of cloudy wet winters (think the Hebrides)
And sunny warm summers (think northern Spain, not Scotland).
In northern California, the wet season may end in April and not start until November.
But the further north you go, the earlier it starts and the longer it lasts.
If you tour the Olympic Peninsula - Forks get 5.5 inches (14 cm) or rain in May.
By comparison, that's an entire spring's rainfall for Edinburgh.
Certainly not the Mojave Desert of your last tour - plus you'll be soloing.
Some years, the wet season last well into June.
The past June was average, June of 2012 was cold and wet, June of 2011 was warm and dry.
Go figure! But May is early regardless.
PS - If you are still addicted to cycling when you get to Southern California,
consider checking into the Betty Ford Clinic, where there is a separate wing for hopeless cycling addicts.