From the tenor of your comments, I suspect that you will find the Seattle area FM radio programming disappointing -- particularly compared to the Boston area. While Seattle has a few good stations, I wouldn't describe them as adventurous. Their programming tends to be very "middle of the road", and if you listen to them long enough, you will find that they repeat a lot of the same pieces.
There are three local FM stations that broadcast jazz, but only one which is dedicated to jazz progamming: KPLU. This station is the NPR-affiliate station at Pacific Lutheran University. This station broadcasts only jazz and blues, with good to very good broadcast quality (depending on where you live in relation to the transmitters). The other two stations which also broadcast some jazz are KUOW and KCMU, but both of these are relatively low power stations. One of the posts above notes that there is a "smooth jazz" station here, which is true, but I think their programming is mediocre at best (if one even considers "smooth jazz" to be true jazz, which I don't).
Sadly, there is only one FM station in Seattle that is dedicated to classical music: KING-FM. The broadcast quality is generally good, but the content isn't very adventurous. However, the MC's for the shows are pretty good, and the station does some live and delayed broadcasts of the Seattle Symphony.
Broadcast quality in Seattle isn't great -- the hilly terrain often results in pockets where the reception isn't very good. The quality of reception on Bainbridge, Vashon, and Whidbey Islands can vary a lot, depending on where you live in relation to the transmitters, so it's pretty hard to generalize. Also, the local stations no longer use high-quality, uncompressed broadcast signals, and rely mainly on "canned" programming.
Last point: as one of the other posts suggested, you should be prepared to invest in a good quality, directional outdoor FM antenna, particularly if you want to listen to the Canadian stations (the closest of which are about 120 miles away).
Steven: If you're willing to stream on your computer, go to KCSM.org. KCSM is the REAL deal. I have not heard a better jazz station. Yes, it is a public station, but it's not affiliated with NPR, so you don't have to sit through 90 minutes of "All Things Considered" during rush hour! They litterally play REAL jazz all day and all night long.
The great thing about KCSM is that all of the DJs have very individualized tastes and styles. It's radio the way it was meant to be. Seriously, check it out.