A significant atmospheric change is anticipated to bring colder and snowier conditions to parts of the United States in the weeks following Thanksgiving. This shift is linked to a disruption in the polar vortex, a phenomenon that affects winter weather patterns. The atmosphere is composed of various layers, with the troposphere being where weather occurs. Above it lies the stratosphere, where strong mid-level winds known as the polar vortex trap cold, sub-arctic air. There are two polar vortexes: one in the troposphere that influences winter weather annually, and another in the stratosphere that contains much colder air but impacts surface weather less frequently. When the polar vortex is strong, the frigid air remains near the poles. However, a weakened polar vortex can allow this cold air to move southward into the U.S. Scientists are still studying these disturbances and their causes, as they can lead to significant cold outbreaks and winter weather events. Sometimes, the polar vortex stretches, resulting in brief cold air bursts and wintry weather. In more extreme cases, a phenomenon called "sudden stratospheric warming" (SSW) can cause major disruptions to the polar vortex. This warming, which may seem counterintuitive, weakens the polar vortex winds, allowing cold air to escape from the North Pole into regions like the U.S., Europe, and Asia. Dr. Amy Butler, a meteorologist with the National Oceanic and Atmospheric Administration, noted that SSWs occur approximately once every other winter. However, she pointed out, "there are only one to two major events in late November in the record back to 1958." Dr. Judah Cohen, a climatologist at MIT, emphasized the unusual nature of the current situation, stating, "We have this unprecedented disruption in the polar architecture where it's so early in the season... There are not many past analogs to draw from and say [with confidence] about how this is going to go." He added that while an SSW is not guaranteed, the polar vortex could still stretch, leading to colder and potentially snowier weather in the U.S. La Niña conditions will also influence this weather pattern shift. Dr. Jason Furtado, an associate professor at the University of Oklahoma, explained that a weak La Niña and other Pacific patterns directly affect North American weather, increasing the likelihood of a colder December. Long-range forecasts from the Climate Prediction Center indicate below-average temperatures for much of the U.S. from late November into December. However, these forecasts reflect average temperatures over time and do not account for short-term fluctuations, meaning there could be brief cold snaps followed by warmer periods. The disturbances in the polar vortex are likely to bring cold air south, increasing the chances for snow. While the relationship between the polar vortex and snowfall is complex, NOAA suggests that this pattern change could lead to more winter-like conditions across the central U.S. and enhance the potential for heavy snow, particularly in the Great Lakes region, known for its lake-effect snow.