The polar vortex, a powerful atmospheric phenomenon, is expected to cause a dramatic shift in weather patterns across the eastern United States. As the vortex weakens and shifts southward, frigid Arctic air will move down into the country, bringing temperatures that could plunge as much as 30 degrees below normal. This extreme cold event will be one of the harshest in recent years, especially compared to the record warmth seen during last year's winter.

The cold air will first affect the north-central United States on Wednesday, with temperatures in Montana, the Dakotas, and Minnesota expected to dip into the single digits or teens. By the weekend, the cold will spread south and east, affecting the majority of the country's eastern half. Over 70% of the US population is predicted to experience freezing conditions, and the cold is expected to persist well into the month, increasing the likelihood of snow.

The polar vortex itself is a persistent feature of the Earth's atmosphere, made up of low-pressure cold air that circulates around the poles. While it generally weakens in the summer, it strengthens during the winter, causing cold air to spill southward into the northern hemisphere. This event mirrors other notable cold outbreaks in history, such as those in 1977, 1982, and 2014. The National Weather Service and NOAA have issued warnings about the upcoming Arctic outbreak, which is expected to bring dangerously low temperatures to much of the eastern US.