No for any area north of SF, even SF in Dec is Yucky Weather in

You would be much much better off only spend your time in Southern CA - any place from San Luis Obispo and South, all the way down to San Diego, is great to travel in Dec.

There are some trails near San Luis Obispo that one can see Monarch butterfly congregating for the winter. I dont remember details but you can google. It supposedly is almost as good as you see it in Mexico.

SF is very rainy and cold in Dec. Seattle is hopeless in winter time, ditto Oregon.

That part of CA/OR/WA should be saved for early Summer, such as late June to late July.