I have lived in 3 states and traveled to almost all of them at some point in my life, but I love living in Washington it is hands down my favorite. If you can get past the rain and overcast skies, it is a wonderful place to live.
UW is the only allopathic medical school in WA so moving here to obtain residency may be somewhat limiting if you are coming from a state with multiple medical schools. That said, only about 6% of UW students come from out of region, so it would definitely be favorable to have in state residence.
Keep in mind that there are tons of residency programs in Washington, and the residency program you attend is a better predictor of where you will practice than the medical school you attend. With that in mind if you get accepted in your home state but not at UW you will likely still have opportunities to come to Washington when you graduate.
If it were me, I would be afraid that I would move to WA and then end up going to a medical school in another state and have to move again. I am not a fan of moving.