A dangerous winter storm is set to affect more than 160 million Americans, bringing intense snow and ice. The cold is expected to be life-threatening, impacting as much as two-thirds of the country, with freezing conditions lingering into February. The wintry weather has been fuelled by activity of the polar vortex slipping down to engulf large parts of the US.
The polar vortex, or Arctic polar vortex, is a ring of strong westerly winds that form between 10 and 30 miles above the North Pole every winter, enclosing a large pool of extremely cold air. When the vortex weakens, its pattern of winds changes from a circular ring to a wavy band that loops further south, unleashing cold weather normally retained at the pole further south. Brett Anderson, senior meteorologist at AccuWeather, compares the phenomenon to a large chunk of ice breaking off a glacier and floating southward with the jet stream.
It is not known whether climate change will affect the polar vortex, says Amy Butler, an atmospheric scientist at the National Oceanic and Atmospheric Administration. There are many factors that can change the strength of the vortex, including sea ice melt and warming in the upper atmosphere, but models show no agreement on future changes. Overall, cold snaps in North America have become less frequent and less extreme, but when they do occur, they can be more dangerous because societies are less well adapted.
Climate change may also influence the type of precipitation, leading to more ice or sleet events in some regions, which could have bigger impacts on transportation. In the western US, snowmelt provides 75% of the water supply, so changes in snowfall could strain water resources. When winter storms do happen, they can sometimes be more intense because a warmer atmosphere holds more moisture that can fall as precipitation.
