
It turns out, a decent plume of smoke from wildfires burning in inland British Columbia got caught up on the northerly flow and was pushed over Western Washington.
Go here to see an animation loop of the visible satellite over the area, taken between 10 a.m. and noon:
The smoke should subside by Monday morning.
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Residing here in the PNW we were a bit perplexed by the weird sky color Sunday, and some people speculated fires but we couldn't place any nearby. So I guess the BC fire factor explains why it was orange all day, but the overall atmosphere of the area has been enduring an especially heavy marine layer throughout the summer to the degree the urban vegetable gardening's not going so well, and June 20th, "Sunday was darkest June day in Seattle in 15 years" [Link]
We had another of those darkest day scenarios a couple weeks ago and people are taking note of how quiet the city seems as if sound is dampened by fog even when its clear.