Not so unusual: Explaining Polar Vortex
Polar Vortex is a 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.
According to a CNN report, here is how the polar 'blast' occurs:
Sometimes,the vortex gets distorted and dip much farther south, allowing cold air to spill southward. 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.
It cannot be compared with tornado or a cyclone. 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.
This phenomenon can happen anywhere in the Northern Hemisphere of earth.
Global warmng could be one of the reasons which cause this air distortion, agrees experts. Global warming can cause extreme distortions of the jet stream, which can cause heat waves in summer and cold snaps in winter.