Sounds like what the forecasters call "foothill winds". I've known it to be quite calm near Carnation and blowing fit to knock limbs off the trees at Falls City and along the David Powell Road. The same thing occurs on the Skykomish along a line somewhere between Monroe and Sultan. It usually begins in mid-morning and lasts until evening. I don't know what the precise meteorological explanation is, but it's the same phenomenon that can occasionally cause hundred mile-an-hour winds in Enumclaw.