What is this thing?

It's a great northern blurred owl. /s ;)

It's really hard to tell without additional information. I would start by grabbing the Merlin app and using the guided search. It will take size, location, habitat, etc. into account and give you a list of things that are most likely. It's free and run by Cornell University so it's safe to use and accurate. It's got a bunch of cool bird ID tools in it if you are into bird identification, so it's neat to have.

https://merlin.allaboutbirds.org/

Probably a great horned owl:

Superb owl

North American Big Boy

https://wdfw.wa.gov/species-habitats/living/species-facts/owls#common-owls

More than a dozen species of owls live in Washington. The great horned owl (Bubo virginianus)(Fig. 1,4) is the species most often seen and heard. It is the most widely distributed owl in both Washington and North America, occupying dense forests, open woodlands, clear-cuts, deserts, and urban environments, including golf courses, cemeteries, and parks with adjacent woodlots. However, except where noted, information about this species applies to most other owls.

That does seem to support an argument for the great horned owl, based on the location. The image there does look kind of like your owl.

It looks a bit stoned?

great horned owl

It's Bigfoot!

Puget Hooter?