Another set of low fares from Seattle to Europe with American Airlines for flight departures early January to March. Fares to most cities are $400s January to March, then $500s to May 10.
These Google Flights links go to lowest fare dates, then use calendar to search other dates for fares.
Even lower fares to the Nordic Countries for winter:
American Airlines Seattle SEA – Philadelphia PHL – Amsterdam AMS – PHL – SEA