The polar vortex is an air mass with cold temperatures and low pressure at the north and south poles that is encased in the polar jet stream. It remains in place year-round and occasionally drifts into regions like Europe, Asia, and North America. While the term has been used by meteorologists for decades, it became popular in 2015 as the entire Northeastern United States plunged into an Arctic blast through most of February. Rochester recorded its coldest February ever, averaging 12.2°.
Defined by its counter-clockwise rotation, the polar vortex over the Arctic Circle is constantly spinning and can provide drastic swings in temperature.
The polar jet stream strengthens and weakens with the seasons, weakening in the summer and strengthening in the winter. We notice more often when it weakens in winter and migrates southward. This can result in those bone-chilling air masses that send us into sub zero temperatures for days on end. A more realistic scenario is when smaller chunks of the polar vortex get chipped off and migrate southward to bring a taste of arctic air that only lasts a day or two.
The polar vortex can send snow to different places, like Spain that saw a piece of arctic cold in mid-January. As the climate continues to warm, the jet stream that holds the polar vortex together will start to weaken. That allows cold air to drift southward and impact different regions. It may seem contrary, but global warming and climate change may lead to more polar vortex “outbreaks” in the coming decades.
Notice three distinct parts of the wavy polar vortex forecast for Tuesday, January 19. The “bubbles” of cold air held in by the polar jet take days to move around and can drift north and south, but rarely do they move further south of 30°N latitude.