Winter camping, or not

Hi, I have read the Winter Camping thread with great interest, as we are starting to head into Fall here (PNW)...and I worry. Hey, it's a hobby. I know to avoid Eastern Wa, if I don't want to deal with the freezing temps, can someone give me a direction for the Western side? How cold is too cold? When do I need to stress over frozen pipelines? We were thinking of sticking to the Olympia/Puget Sound area, but I'm wondering if we need to head to CA instead...