The Grand Canyon stuns visitors with breathtaking view every day. Between November 29 and December 2, 2013, it stunned visitors even more – by not being visible. A rare meteorological event filled the canyon with an ocean of clouds. Such events are so rare that the National Park Service Rangers, who see the canyon every day, wait for years to see the ground-hugging fog.
The Moderate Resolution Imaging Spectroradiometer aboard NASA’s Terra satellite captured a true-color image of this rare event as it flew over the Grand Canyon on November 30. A thick white fog (low cloud) fills the upper Grand Canyon, while higher elevations remain clear. Scrolling over the image will reveal the scene captured by the MODIS instrument aboard the Aqua satellite on December 2, when almost all the fog has dissipated.
The fog was trapped in the Canyon by a temperature inversion, which happens when the air near the ground is cooler than the air above it. A high-pressure system brought low temperatures, clear skies and calm winds to the Grand Canyon. During the log nights, the ground cooled quickly, chilling the air immediately above it. The air higher in the atmosphere did not cool as quickly, so an inversion developed. Without wind to stir it, cold dense air was trapped beneath a more buoyant layer of warm air.
The inversion was only part of the story. A few days earlier, a winter storm dumped heavy snow and rain on northern Arizona. The National Weather Service reported 11.5 in (19.2 cm) of snow at the Grand Canyon. The snow and the rain left the ground and the air above it very moist. As the air near the ground cooled, the water condensed into fog, which was trapped in the canyon by the temperature inversion. While temperature inversions might happen a couple of times a year, it is rare for so much of the canyon to be enveloped in fog.