The wildfire smoke hung low over 77-year-old Lynda Raymond's Maple Leaf neighborhood last week, suffocating the place. No one was out on the streets, everyone's window was shut, Raymond said, mourning the lost week of late summer. The smoke mingled with the fog in the mornings, silencing the neighborhood. That's when she heard the foghorn.
The sound blared repeatedly. It didn't sound close from up on the crest of Maple Leaf, the third-highest point in Seattle, Raymond said, but it didn't sound far away either. The sound reminded Raymond of the 30 years she spent in Vancouver, British Columbia. But she'd been close to the port then. Maple Leaf wasn't anywhere near the water.
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Residents all around North Seattle reported the same sound. One man heard it north of Raymond in Pinehurst. Jean Sherrard, who writes a weekly column for the Seattle Times, heard it in Greenlake for the first time last Sunday.
He described the sound as "several low toots at least, separated by a minute or two."
"The first toot, actually, I assumed was that of a distant train, the horns of which can be heard on a still evening when the wind is right," Sherrard told me in an email. "But unlike a train, the low hoot of the foghorn contains no harmonies."
Everyone I talked to was sure the sound was boat-related. Absolutely nautical. But nobody could say for sure what they heard or why. I figured it out.
A comment on a NextDoor post posing the foghorn question (what's the deal with these foghorns?!) suggested that sound traveled further because of the smoke and fog. Sure, that seemed plausible. I called the forecasters at the National Weather Service in Seattle.
"Sound traveling further in smoke?" The forecaster on the line asked. "I've never heard of that." He suggested I talk to the scientists at the University of Washington.
I fired off some emails to some post-docs in the department of atmospheric sciences. Almost immediately, as if it was his life's calling, Dr. Joe Zagrodnik, a post-doctoral researcher, responded.
"This is almost certainly the result of sound ducting under a temperature inversion (the same one keeping the smoke trapped at the surface)," Zagrodnik wrote in his email.
An inversion—he had to explain to me in a follow-up—happens when a layer of warm air sits on top of a layer of cold air and doesn't mix; like oil and water. The sandwiched cold and hot air traps the sound, causing it to bounce around in there and then back to the ground, which amplifies it, Zagrodnik explained.
Inversions aren't rare. They mostly occur on calm nights or on winter mornings before the sun rises. But, the smoke hellscape created an abnormal temperature inversion. Zagrodnik said the smoke "is probably strengthening the inversion—the smoke is absorbing the sun's rays and heating the atmosphere in the warm layer instead of heating the earth's surface."
The smoke also sits higher off the ground than a normal inversion, which makes this situation unique. "I'm guessing that has something to do with the sound reaching the higher hills like Pinehurst," Zagrodnik said. During an inversion, the speed of sound is higher at higher altitudes.
So the smoke trapped high in the air bounced a foghorn sound all the way from somewhere in Western Washington's waters to the high hills of Northern Seattle. But what made those sounds?
According to Captain Jill Russell, a longtime professional mariner, the International Regulations for Preventing Collisions at Sea gives specific guidelines for how boats should act in restricted visibility situations like fog, mist, snow, or even sandstorms. Those rules change depending on the vessel and the work the vessel is doing, but general guidance for power-driven vessels in Puget Sound, Russell said, is to make one prolonged blast (four to six seconds) no less than every two minutes.
Peter McGraw, a spokesperson for the Port of Seattle, suspected those blasts could be from the ferries since "they’re the ones that are traversing the waterway most frequently."
Ian Sterling, a spokesperson for the Washington State Ferries, shot that theory down. Ferries have "a fairly distinctive whistle" that don't really sound like a foghorn, Sterling said. Plus, he said, "North Seattle doesn't have a lot of ferry runs that go near there. I’d be surprised if [the mystery sound] was ours."
Nine miles from Lynda Raymond's home at the crest of Maple Leaf is the West Point lighthouse, just south of Shilshole in Discovery Park. When it's foggy, the lighthouse makes a 1 second blast every 10 seconds, Russell said.
She searched for other aids to navigation (ATONs) on Lake Washington with an associated fog signal but couldn't find anything. While any of the boats criss-crossing Lake Washington and making their required fog bleats every two minutes could have made the sounds, Russell said, she suspected it was the lighthouse.
"It would have to be the West Point light if the folks in Maple Leaf were hearing the signal every 10 seconds," Russell said. "Hard to know without hearing it myself or knowing the duration of the blast."
The smoke is gone and with it, presumably, is the foghorn sound. The fall fogs, however, will roll in. Whether those fog alerts will get to North Seattleites remains to be seen. Maybe that's just a special something they can only expect during climate change-fueled events.
"The foghorn just added a melancholy voice to the gloom," Jean Sherrard described. "And yet somehow a comfort as well—as if to say, yup, you’re all alone, buster… but not really. Someone else somewhere else is searching for safe harbor, even if the search engine is antique (like echo-location)."