Air grafted grape

I air grafted a grape vine last spring.  Now on Oct 1st, it has a nice root ball and I have planted it in a 1 gallon pot.  My question is, what should I do with in over the winter?  Should I just leave it outside, or do I need to bring it indoors when the weather drops below freezing?  I plan to plant it in the spring here in the Seattle area.
Thank you!

If it's already got a good root ball I would just put it in the ground over the winter. I've had most success with starting grapes in the ground in their final spot. They seem to have no problems with winter.