With the recent cold, the term “polar vortex” has been everywhere. What is the Polar Vortex? According to the National Weather Service, the polar vortex is a large area of low pressure and cold air surrounding both of the Earth’s poles. It ALWAYS exists near the poles, but weakens in summer and strengthens in winter. The term "vortex" refers to the counter-clockwise flow of air that helps keep the colder air near the Poles. Many times during winter in the northern hemisphere, the polar vortex will expand, sending cold air southward with the jet stream. This occurs fairly regularly during wintertime and is often associated with large outbreaks of Arctic air in the United States. One particularly strong incursion occurred in January 2014, when Manhattan last saw subzero temperatures. Other cold outbreaks that have occurred in the past, also link to the polar vortex, occurred in 1977, 1982, 1985 and 1989. In December 1989, Manhattan recorded two of its top ten coldest readings: -21 oF on December 21st and -22 °F on December 22nd.
Mary Knapp, Weather Data Library