I dont think it's Washington. Looks more like a flight to Asia passing by Alaska. Most flights to Asia skim Alaska coast.
Cannot confirm, but there is too much water, and not enough land (green land/trees) for it to be Puget Sound. Looks like a northerly view towards Alaska from a passenger airliner. It just does jive with my personal flight time in the NW, but does look like a view on the long voyage to Asia.
I've flown around the area for decades and it just looks strange to me,ie, not Washington but likely Alaska.
It could be confirmed with weather history.
I don't recall that much cloud cover in Wash. that day, though there was scattered coverage. It's also a strange pattern of cover for this area in Wash. this time of year.