How to fill the Grand Canyon with clouds
The science of inversions
During the wintertime, weather forecasters sometimes get things spectacularly wrong. They predict a bright, sunny day, and instead you get a day of dense fog and misery. The culprit? Almost always an inversion.
You probably already know that temperature normally decreases with height. Warm air is created at the surface as the Sun’s rays hit the ground, while colder air sits on top of it. However, cold air is denser than warm air, making the atmosphere inherently unstable. If it weren’t for this fact, we wouldn’t have weather at all — our atmosphere would settle out over time, like a vinaigrette.
But sometimes, due to the movement of air masses around the world, warm air can end up sitting on top of cold air. This happens close to warm fronts, and also in areas where very cold water is coming up from the bottom of the ocean, like the Californian coast. When this happens — when warm air is sitting over colder air — the atmosphere becomes very stable, and we call it an inversion.
That’s what happened at the Grand Canyon this week. A winter storm passed through the area in late November, leaving frozen ground and cold, humid air behind it. Then, when a warm air mass moved over the top, the cold air was trapped below. The water vapour in the cold air condensed and turned into fog.
The freezing fog coated the bottom of the canyon with ice, covering trees, bushes and rocks with a layer of frost known as rime. This thin coating tends to burn off quickly once the fog disappears.
Smaller inversions do occur quite frequently in this area in the wintertime, but it’s very rare for one to affect the entire Grand Canyon due to its sheer size. Park rangers posted on Facebook that they “wait for years to see it”, adding that this kind of event only happens once a decade.
You can see the canyon clouding over in this video, shot at dawn on 29 November 2013 from Mather Point by Paul Lettieri:
Looking Up is a collection on Medium that offers a home for those obsessed with the world above our heads. It’s curated by @duncangeere. If you enjoyed this article, please click the “recommend” button below, and if you want more, then click the “follow” button to make sure you don’t miss anything we publish in the future.
