You don't have to be a registered member of a political party to caucus. You just need to be a registered voter. Your vote in the primary will not decide anything if you are a Democrat, as all the delegate allocation will be done during the caucus. The Republicans are allocating half during the caucus and half during the primary.
Here's a FAQ from the Seattle Times with more.
Find your Democratic caucus location
Find your Republican caucus location: King Pierce Snohomish.
Go democracy! See you on Saturday!