Americans in two dozen states from the Midwest to the Southeast and Northeast are shivering this week courtesy of a distorted polar vortex . The rush of cold air it 's sending southward is the biggest visitor from the North Pole since Santa Claus . The gifts it brings , however , are chilling and generally unwelcome . Much of the United States has plunged into a deep freeze from record low temperatures . CNN International senior meteorologist Brandon Miller answers a few pressing questions about this phenomenon . What is a polar vortex ? What distinguishes it ? The polar vortex , as it sounds , is circulation of strong , upper-level winds that normally surround the northern pole in a counterclockwise direction -- a polar low-pressure system . These winds tend to keep the bitter cold air locked in the Arctic regions of the Northern Hemisphere . It is not a single storm . On occasion , this vortex can become distorted and dip much farther south than you would normally find it , allowing cold air to spill southward . How frequently does this polar vortex distortion occur ? The upper-level winds that make up the polar vortex change in intensity from time to time . When those winds decrease significantly , it can allow the vortex to become distorted , and the result is a jet stream that plunges deep into southern latitudes , bringing the cold , dense Arctic air spilling down with it . This oscillation is known as the Arctic Oscillation and it can switch from a positive phase to negative phase a few times per year . This oscillation -- namely the negative phase where the polar winds are weaker -- tends to lead to major cold air outbreaks in one or more regions of the planet . Where on Earth can this happen ? The polar vortex can lead to major cold air outbreaks in any portion of the Northern Hemisphere -- North America , Europe and Asia . This will lead to cold snaps in multiple locations , though not always . How dangerous is a polar vortex distortion as compared to a tornado or hurricane ? Completely different type of systems . A cold air outbreak caused by the polar vortex is much more widespread and lasts longer than a single storm . With the widespread drop in temperature , however , you can see significant winter storms develop , especially when the cold air is initially advancing into a previously warm region -- much like the nor'easter this past week . When was the last big one to hit a densely populated area ? Serious cold snaps happen several times a year , though in different regions of the world and with different severities . Last March saw a significant decrease in temperature as a result of the polar vortex pushing into much of Europe . Many locations experienced an Easter holiday that was much colder than their Christmas holiday . The United Kingdom , for instance , had its coldest March in 50 years . If you get caught up in one , what should you do ? Again , it 's not a `` storm '' that you get caught in . But when faced with significant cold temperatures , you should stay inside whenever possible , layer clothing if you must be outside , winterize your home and car , etc . Is it a side effect of global warming and should we expect more events like this ? This is a hotly researched topic . In short , yes , it could be . It seems counterintuitive that global warming could cause significant cold snaps like this one , but some research shows that it could . We know that different types of extreme weather can result from the overall warming of the planet , melting of the Arctic Sea ice , etc . This includes extreme distortions of the jet stream , which can cause heat waves in summer and cold snaps in winter . Parts of Western Europe have been battered by the worst storms for two decades during the past week -- are they related to the weather system in the United States ? They are related in a sense , but I would n't say `` caused by . '' The storms in Europe are the result of a persistent pattern that has seen the jet stream parked near the United Kingdom and Ireland , which has brought a train of storm systems over the British Isles . This is the same jet stream , of course , that has plunged deep into the southern portions of the United States . So , the jet stream has been `` stuck '' in a position that is allowing cold Arctic air to spill into much of the United States and Canada . But it is in a position that is bringing warmer , moist air from the Atlantic over Northwest Europe , resulting in the stormy conditions .
Polar vortex is circulation of strong , upper-level winds that normally surround the North Pole . The distortion can lead to major cold air outbreaks in North America , Europe and Asia . A cold air outbreak caused by the polar vortex is much more widespread than a single storm . Research suggests the distortion could be a side effect of global warming .