As temperatures hit triple digits, a zoo keeper at Henry Doorly Zoo in Omaha, Neb., cools off a Double Yellow Headed Amazon parrot with water spray, Wednesday, July 20, 2011. For millions of people ... more 
As temperatures hit triple digits, a zoo keeper at Henry Doorly Zoo in Omaha, Neb., cools off a Double Yellow Headed Amazon parrot with water spray, Wednesday, July 20, 2011. For millions of people suffering through the breathtaking heat and humidity gripping the nation’s midsection, it may feel like they’re living in a pressure cooker. And in a sense, they are. The heat "dome" sitting over much of the U.S. is caused by a huge area of high pressure that's trapping and compressing hot, humid air from the Gulf of Mexico beneath it and pushing the jetstream _ and thus cooler, drier air _ far northward into Canada. (AP Photo/Nati Harnik) less 
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Associated Press | Photo By Nati Harnik
Wed, Jul 20, 2011 5:57 PM EDT