Before I deal with the main blog topic, I would like to ask those of you in North Seattle to be on the look out for a lost black/while cockapoo: information is here. Thanks for any help.
During warm days there is a profound change in winds up and down the Olympics that is normally invisible, but become apparent when there is a wildfire on the Olympic slopes.
Dale Ireland has a wonderful permanent cam facing the Olympics and has been recording the smoke from the Big Hump fire the last few days.
Here is a video for a few days ago: http://www.drdale.com/lapse/lapse110906s.mov
This one is also good: http://www.drdale.com/lapse/lapse110903s.mov
During the day, as the slopes are heated there is upslope flow moving towards higher elevations--this upslope flow and the destabilization of the atmosphere as the mountains heat up produces convection and enhanced upward flow. Sometimes this convection is accompanied by a cumulus cloud as well as smoke (called pyrocumulus). The rising air cools due to the expansion of the upward-moving air and eventually the initially warm air is no longer buoyant (becomes the same temperature as the environmental air at that level) and no longer rises. You see this all the time from smoke from smokestacks hitting a level through which it can pass and then spreads mainly horizontally--check out this picture:
During the evening, the surface of the mountains cools as the infrared radiation loss to space exceeds the incoming energy from the sun. The daytime convective/smoke plume dies (since it depends on the surface being sufficiently warmer than the air above), and air starts moving down the mountain....known as downslope flow. The smoke is entrained in this flow and heads down the slope. That is what you are seeing.