Most of the smoke is coming from fires in BC delivered to the south by the prevailing north winds. It blew into WA state yesterday morning. The change was pretty dramatic as the satellite images show.
http://cliffmass.blogspot.com/
That is what the news states & may be partially true, however with the predominately east winds blowing here in OR, I suspect most of our smoke is coming from the active forest fires east of the Cascades in WA & OR would be the more accurate.