The polar vortex is stirring up, bringing the earliest hints that the weather is changing with the new fall season. The polar vortex is a swirling mass of frigid air high in the atmosphere, always present near the Arctic. A weaker vortex increases the likelihood of Arctic air reaching the U.S., while a stronger vortex generally keeps the chill locked farther north. In other words, the polar vortex signals potential cold approaching, but does not guarantee a brutal winter. What does the polar vortex look like right now?