Smoke

It's subtle...but perhaps you noted some visibility degradation, particularly if you looked east towards the Cascades...I suspect is it is from all the fires burning over the Rockies and a few to our south.

Here is the latest picture looking towards Mt. Rainier from the UW...hard to see the mountain and the rest of the crest.  Yesterday around noon the haze/smoke was really obvious from the air when I flew into Sea Tac around noon.

 Here is a visible satellite picture this morning...you can see the smoke a bit...stretching from the Willamette Valley through northern Idaho and Montana.

 Take a look at the current major fires.  Lots of them over the Rockies.   I suspect this smoke has been moved around by the upper-level flow, but I have not done any trajectories yet to prove this.

 Currently, a fairly major fire (Dale) is burning near Redding, CA (about 1200 acres).  This should be a fairly calm year for wildfires here in the NW, since surface moisture is above normal as has been the snowpack.