Welcome to the great Pacific Northwest! One of the best lily growing regions in the WORLD!! hehe

I'd keep your lilies potted and kept in a cold area that does not freeze and thaw constantly. An unheated garage or cellar or even a protected area outdoors where you can throw an old blanket over them when it's freezing will work well. Hopefully, the potting mix you have for them drains well as this will be key in getting them through the winter. They need some moisture, but not too much.

Key thing is to keep them cool and evenly moist, but not too moist and they'll be up and going again next spring. Also, be sure to cut off those stems when they brown up so they don't attract any critters.

Hope this helps a bit

Riz