2/3rds of the wineries in Washington are east, way east, so If you're going to be in Seattle or the Puget Sound you'll only have a couple of choices.
Yakima is the first major city with some volume (Hogue). Ch. St. Michelle is a good one to vist and close to Seattle and has alot of great reserve wines and sparkling.
http://www.ste-michellewines.com/win...vingDirections
In the Northwest (Oregon included) Memorial day and Thanksgiving tend to be the largest event days at wineries. If you're into travelling then I can send some Yakima/Tri Cities or Walla Walla recomendations, but that is a long drive from Seattle. However check out the list from this website for wineries in the puget sound.
http://www.winesnw.com/pugetmap.html
(My wife is a GM of a winery in Oregon)