March may seem late for a blizzard, but the storm hitting Washington, D.C., today has its roots at the North Pole in early January. Usually, cold air in the stratosphere swirls around the pole, trapped in a vortex spinning about 5 miles above Earth's surface. This year, however, the red mass of warm air traveling up from Siberia burst through the blue concentric circles of the polar vortex on 7 January, pushing cold air down to lower latitudes as seen in the animation above. This rare event is called a major stratospheric warming, and it's no coincidence that severe winter weather began in the United States about 10 days later, says meteorologist Judah Cohen of the company Atmospheric and Environmental Research in Lexington, Massachusetts, who helped create the animation with funding from the National Science Foundation. "What happens in the stratosphere translates all the way down to the surface," leading to more snowstorms and lower temperatures in the United States and Europe, he says. So where did that red blob of warm air come from in the first place? Scientists still debate the origins of stratospheric warmings, but Cohen believes that this year's event can be traced back to increased snowfall in Siberia, which intensified the temperature difference between the oceans and the Eurasian continent and created a wave of energy that rushed toward to the pole. Any lingering effects should be tapering off soon, Cohen says—but for those of us in Washington, it won't be soon enough.