Ok, this is not exactly the kind of music you were asking about, but it is what I equate to summer: picnic on the lawn, chamber music, summer nights...
Ahhhh.
Here is the link: http://www.seattlechambermusic.org/index_flash.html
Consider taking a picnic and listening (for free) from the lawn, or supporting the arts and buying tickets for the season. Also, there is an incredible evening of young artists that will amaze you.
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