The polar vortex might sound like a pretty dependable natural system for regulating each hemisphere's climate. But in practice, it doesn't quite run that smoothly. For one thing, its shape typically is a bit irregular in its boundaries, with areas known as troughs where the cold air extends away from the pole, and other areas called ridges, where the warm air pokes toward it [source: Serreze].
Additionally, the high-speed winds that form the polar vortex's barrier can change in intensity from time to time. If the winds weaken too much, that can distort the vortex and make its boundaries even more irregular, so that a whole lot of cold air heads southward into places that don't normally get it [source: Duke].
While the polar vortex might seem like a shocking new phenomenon, cold snaps caused by distortions in the vortex actually have happened at other times in recent history. Back in January 1985, for example, the northern polar vortex was really distorted, and polar air pushed southward into the eastern U.S. In normally balmy Florida, the plunging temperatures destroyed 90 percent of the state's citrus crop. In Washington, D.C., the parade and outdoor ceremony for President Ronald Reagan's second inauguration had to be cancelled. Worse yet, at least 126 people died from the effects of the cold [source: NOAA].