Over the past several days, the eastern two-thirds of the continental United States has endured bitterly cold temperatures associated with the southern plunge of a continental Arctic air mass, fresh from the plains of Canada. With the bulk of the Great Plains still covered in snow following the Christmas holiday blizzard of 2009, little moderation of the cold, dry air mass has occurred. Temperatures have been up to 15 degrees below normal, and these cold temperatures will dive southward through the opening days of 2010. The CIRA Total Precipitable Water Anomaly product outlines the coldest, driest core of the air mass (dark brown) through Missouri and the Dakotas, while dry air remains in place over the Southeast from a previous surge of Arctic air last week. Meanwhile, atmospheric moisture is limited to the Pacific Northwest while the core of the United States remains dry.