A cold snap is likely on the way for millions of people across the northern US. It's due to strike shortly after Thanksgiving, meteorologists say. The cause: the weakening of a weather pattern known as the polar vortex. Think of an ice skater spinning in place on the ice. The faster she twirls, the easier it is for her to maintain her balance. She can keep her arms tucked tight. As she slows down, she’s more likely to topple over. Her arms flail out for balance. The polar vortex works in a similar way. It relies on the jet stream. That's an air current that runs west-to-east across the Northern Hemisphere. The faster the jet stream blows, the better it can contain all the cold air trapped at the North Pole. When the jet stream slows down, icy Arctic air can leak southward. Weather patterns exist in the layer of Earth’s atmosphere called the troposphere. The impending chill is caused by changes in the layer directly above it — the stratosphere. “Even though the ... polar vortex is miles above us, it’s sometimes connected to our weather via invisible puppet strings we describe with atmospheric dynamics and thermodynamics,” meteorologist Andrea Lopez Lang told CNN. In this case, it’s all about those thermodynamics. It's a term that means the movement of heat. A sudden rush of warm air into the stratosphere above the North Pole is weakening the polar vortex. That should cause all that chilly weather to leak southward. It will blanket much of the US in colder-than-average temperatures through the first few weeks of December. And while scientists aren’t sure why these sudden warming events happen, they do note that it’s extremely rare for them to occur so early in the winter weather cycle. Reflect: What is the coldest weather you’ve ever experienced?
