SSW is one of the most radical changes of weather that is observed on our planet. It’s a rapid warming (up to about 50 °C within a week) in the stratosphere, between 10 km and 50 km up. This phenomenon is caused by atmospheric waves that originate in the troposphere.
SSW events can occur anytime from late November through March. They can displace or split the polar vortex; they begin weakening the polar vortex and if it displaces or splits into two separate polar vortices, one which moves over North America and the other sets up over the Eurasian continent, and can send the coldest air in the northern hemisphere southward.
Currently we can reliably predict individual SSWs about a week in advance, and we can detect them early on with satellite and other observations.