A Boeing F-15SA development airframe has been in the PNW. The F-15SA is a development of the Strike Eagle family specifically for the Royal Saudi Air Force. They are buying new jets as well as updating the F-15S jets they bought years ago. Production jets have been delivered for a while now but testing activities continue. I had heard that a jet was at Boeing Field for a while and had even seen the tails parked on the ramp as I drove by but I hadn’t seen it moving.
Military jets don’t usually show up on the mainstream flight tracking apps (but this one had when it traveled cross country) so I didn’t know it was airborne. However, I heard it call up on approach so stopped what I was doing and grabbed the camera. Sure enough, it came zipping down the approach. A few quick shots and then it was down. Apparently I was rather lucky. A couple of days later it headed back across country.