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Environment

When Heaven Descends, the Grand Canyon Fills With Fog

ImaGeoBy Tom YulsmanDecember 6, 2013 6:16 AM

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Image of the Day

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The view from Mather Point at sunrise in Grand Canyon National Park on Nov. 29, 2013. (Photo: © Paul Lettieri) I've explored the Grand Canyon's inner recesses on hiking and backpacking trips at least a half dozen times. I've seen it under a hot summer sun and with a blanket of snow. But even after all of those experiences, I never would have guessed that this photograph was taken there. It was, in fact, the sunrise view from Mather Point at the South Rim as fog filled the canyon on November 29. The photograph was taken by Paul Lettieri, who kindly allowed me to share it here. You may have already heard about this once-in-a-decade event, which received quite a bit of coverage starting the day after Thanksgiving. But you probably have not seen some of the following imagery that I've put together, including an amazing time lapse video, once again courtesy of Paul Lettieri, and also some remote sensing views. So keep reading... http://youtu.be/DfZKZGtdmOg ©2013 Paul Lettieri For more of Lettieri's images, check out his Flickr page and also his website. The fog first began filling the canyon on Nov. 29th. During the warmth of the day, it burned off — only to return again on the 30th. And again on Dec. 1st — and once again on the 2nd. Here's how it looked to a GOES weather satellite: http://www.youtube.com/watch?v=a4UnqHuYZA4 The Grand Canyon wasn't the only part of the West to experience fog during this period, as this animation of satellite images shows:

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The extent of fog and stratus clouds in the Four Corners region and beyond is seen in two images captured on Nov. 30th by the VIIRS instrument on the Suomi NPP satellite. One is a natural color view, the other in false color. The red is indicative of snow. (Source: CIMSS) These two images, both acquired by the Suomi NPP satellite, show the incredibly widespread extent of fog and low stratus cloud over the Four Corners states of Arizona (lower left), New Mexico (lower right), Colorado (upper right) and Utah (upper left) on Saturday, Nov. 30th. Snow cover shows up as a brighter white color in the true-color view, and red in the false-color image. (When fog lifts above the ground it is technically called stratus.) This rare event was the result of a complex set of conditions that came together in just the right way. As I reported in an Image of the Day post before Thanksgiving, a winter storm had dumped a lot of snow on this part of the West, including the Grand Canyon. The precipitation left the ground quite wet, as well as the air right above it. Then a ridge of high pressure moved in and decided to hang around for a few days, causing clear skies, cold temperatures, and calm winds to settle in with it. Under these conditions, the ground cooled significantly during the long nights. Since colder air holds less moisture, water condensed. But that on its own wouldn't have been enough to result in extensive fog. One other ingredient was needed: Something to keep the condensed moisture — clouds, essentially — from dissipating. In other words, some kind of cap to keep it all down by the ground. That capping was provided by a temperature inversion — a common occurrence in winter under high pressure conditions. It's pretty simple: The air right above the ground cooled at night more quickly than air higher up. This is because air is not a particularly good conductor of heat. The result: Cold, dense air by the ground, capped by warmer, more buoyant air higher up. Add in the fact that there wasn't much wind to stir things up and you have a terrific recipe for fog and low stratus clouds.

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