Why Was Christmas So Cold This Year?

It was a frigid Christmas in much of the United States.

Chicago and Minneapolis both experienced their coldest December 25ths in decades. Erie, Pennsylvania weathered a stunning lake-effect storm that dumped more than 4 feet (1.2 meters) of snow on the city, shattering state records and prompting the local government to declare a snow emergency. And both Portland, Oregon and Seattle had a rare white Christmas.

The below-average temperatures are the result of a mass of Arctic air "buckling" southward from northern Canada toward the eastern U.S., said Robert Oravec, a lead forecaster at the National Weather Service's Weather Prediction Center.