Why more frequent cold blasts could be coming from global warming

Frigid air that normally stays trapped in the Arctic has escaped, plunging deep into the United States for an extended visit that is expected to provoke teeth-chattering but not be record-shattering. Meteorologists say it's because the jet stream — that usually west-to-east river of air way above ground that moves weather systems along — has made a roller-coaster like dip from the Pacific Northwest to the Southeast and is stuck on that wavy track. To the west of that plunge, in California, it’s hot and dry. But to the east and just above the dip, it’s a taste of the North Pole. It’s a cold air outbreak that some experts say is happening more frequently, and paradoxically, because of a warming world.