For the past week Seattle has been stuck in an inversion. Under these conditions, our weather is particularly miserable, cold and foggy. In addition, the air gets really stagnant, which causes poor air quality and associated public health effects. To be clear (because I’ve overheard a lot of people getting this wrong), the inversion is not caused by pollution–it would happen even if there were no Seattle. However it does worsen pollution because fresh air isn’t getting mixed in.
During an inversion, the sun is a distant memory. It’s a little extreme even for Seattle, and so on Saturday, Andrew and I decided to hike above the clouds where it was sunny and warm.
Poo Poo Point via the Chirico Trail
Distance: 4 miles round trip
High Point: 1850 feet above sea level
Elevation Gain: 2200 feet
Highlights: Being above the inversion, sunshine, awesome clouds, Mount Rainier.
Low points: Ever since Jasper the Dog was attacked by an off-leash dog in our neighborhood, he’s been much more aggressive around other dogs … and there were a ton of dogs on the trail. Poor pup. Hiking used to be one of his favorite activities.
An inversion in the atmosphere occurs when temperature increases with height, or in other words the ground is colder than the overlying air. This configuration inhibits air from rising, because the cold air is very stable (not buoyant). Inversions can be caused by two mechanisms, both of which are tied to high-pressure weather systems. 1) Because high pressure is associated with clear skies, the ground can very effectively radiate heat to space, and so the ground cools. 2) High pressure is also associated with sinking air aloft, which leads to compression of the air and thus warming aloft.
So we have a situation in which moist, cold air is trapped near the surface, and that leads to epic fog. The inversion prevents air mixing in from above and dissipating the fog. To make matters worse, at this time of year and this latitude, the sun is weak; the fog won’t simply burn off. It lingers.
It can get a little depressing if you’re stuck under the cloud. But above, it’s glorious.