Apparently this only happens a couple of times a year in the Grand Canyon, and only about once a decade as significantly as it did yesterday.
Photos from the Grand Canyon facebook page are shown on this Daily Mail page.
http://www.dailymail.co.uk/news/article ... menon.html
For those with a FB account, you can find them there as well at https://www.facebook.com/GrandCanyonNationalPark
Woulda been a great day to be there yesterday! I especially like the views of the desert facade from Desert View. Comanche Point out to Cape Solitude with clouds in the canyon below? Awesome!