A number of local media outlets produced stories about this unfortunate fragrance, such as the Weekly and the Stranger.
Twitter was full of complaints, some perhaps not suitable for a younger audience.
The smell was not limited to Seattle but was also noted on Bainbridge Island and north/south of the city.
My curiosity aroused, I starting looking into this relatively unusual situation.
The meteorology was favorable in many ways. With high pressure building over the region, a very strong low-level inversion (temperature warming with height) developed over Puget Sound. Here is the plot at Seattle for a few hours last night. There was a shallow cool layer 100-200 meters thick which contained the fog and strong warming (the inversion above)
And then there were the winds...they were very weak (as shown by this plot around Seattle around 4 AM, the circles with dots in the middle indicate calm winds). Weak winds produce little turbulence and vertical mixing. That helps keep smells in.
I checked with Seattle Public Utilities... there was no sewer outflows/spills and they said that was true for King County. The winds were weak, so there was no reason to expect strong air flows from regional pulp mills.
But there was something different this time....we just had major flooding...not in Seattle, but in communities to our east. Flooding followed by relatively warm temperatures.
It seems logical. Large areas were covered with water and during the last day the water had receded. Some of it farm land. Manure and some sewage got spread over it. Might the there have been the release of SO2 (sulfur dioxide) as the moist land stewed a bit in the warm temperatures yesterday?
Smell generation area?
As a check, I looked at the air trajectories (3D air paths) in the UW high resolution model; specifically 24h trajectories ending 10 PM yesterday. The air came from the east side!
I talked to James Rufo Hill of Seattle Public Utilities and he thought the flooded ground idea was a reasonable hypothesis. However, such smell scenarios are bit out of my area of expertise (thank god!), so I will leave this to my readers to push this further.
And keep in mind it could have been worse. In fact, there is a movie (The Fog) about an unusual fog in Oregon that brought not only unpleasant odors, but zombies as well. I will be content with the smell.