Seattle is another airport with airfare down to $400s to several cities across Europe including Frankfurt, Munich, Zurich, Amsterdam and Brussels across all three alliances. There are also discount fares to Scandinavian airports Copenhagen, Gothenburg and Stockholm.
Lowest fares are available February to May.
Dates are searchable on Google Flights and lower fares are found through Momondo.com meta-search for online travel agency ticket discounts.
British Airways Seattle SEA – London LHR – Frankfurt FRA – LHR – SEA
United Airlines Seattle SEA – Zurich ZRH – Seattle
Delta Airlines Seattle – Amsterdam AMS – Seattle
This Delta fare is an example of what I found on Google Flights at $468. Then I entered these dates into Momondo.com and a KLM fare came up for $40 less. Using Google Flights to locate low fare dates and then checking Momondo.com for even lower fares on these dates is a search strategy I find effective.
KLM Seattle SEA – Amsterdam AMS – Seattle
$428 Citiair.com ticket round trip Sun Feb 19 – Sun Feb 26