Weather mystery: A stinky fog envelops Seattle

Fog rolls into Seattle the evening of Jan. 6, 2015, courtesy Twitter user @aspseattle37

SEATTLE -- The fog that rolled in last night over Seattle was a sight to see...

But not a sight to smell, apparently.

Social media was full of reports last night around the heart of Seattle into Queen Anne, North Seattle and Capitol Hill of the fog smelling quite bad, with descriptions ranging from rotten egg to sewer to pulp mill.

In checking the data, we can see why a smell would be trapped across the city: There was a very strong and very low inversion right between 4 p.m. and midnight Tuesday night as the fog rolled with an atmospheric "lid" at just paltry 300-400 feet. Thermometer sensors at the University of Washington showed the temperature was about 3-4 F warmer at 300 feet than at the surface -- that's enough that the top of Queen Anne would be 4 or so degrees warmer than just going down to Myrtle Edwards Park.

As for what caused the smell, it's still a mystery. Seattle Public Utilities says their crews have responded to five calls in the past 24 hours for strong odor -- all around the Ballard/Greenwood and Phinney areas, and found no issues with drainage infrastructure.

Some suggest it might just be stinky maritime sea smell that pushed inland, like a low tide smell? But it wasn't really low tide at 4 p.m.:

Image courtesy: NOAA

A nearby pulp mill could also explain the sulfur-type smell descriptions but there aren't any in North Seattle. And officials with the Puget Sound Clean Air Agency said there were no obvious registered sources in those areas that would make a sulfur smell.

Another theory tossed out there from Seattle Public Utilities is perhaps run-off from rivers that flooded upstream during Monday's heavy rains may have picked up something smelly and dumped it into the Duwamish Waterway.

The Duwamish Waterway is running quite cloudy right now, but if you're thinking it's sewer-related, SPU officials said it's highly unlikely it'd be any kind of sewer overflow, which actually would not make that kind of widespread smell.

But come to find out there are now reports of the smell a bit beyond Seattle. Kitsap County is chiming in as well. A map from the Puget Sound Clean Air Agency does show that the general air flow, while weak yesterday, did originate from eastern King County where there was recent flooding (the green line traces back inbound air flow to Seattle over past 36 hours):

So maybe the foul smells are from leftover flooding gunk in the warm sun in eastern King County, drifting into the Seattle area then getting trapped and compressed under the strong inversion that quickly developed over Seattle Tuesday evening? That is the leading scenario at this point. That would also explain the continued westward drift into Kitsap County.

Whatever it was, that kind of atmospheric lid would certainly trap any pollutants right near the ground with little to no ventilation. So the smell would have nowhere to go vertically, and instead spread out horizontally near the ground.

I'll be updating this story if we get more information -- a number of Seattle/King County agencies are on the case!

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