Communities across the eastern United States are facing severe winter weather in the coming days and weeks, as a fractured polar vortex sweeps south, bringing with it colder than normal temperatures.
Mark Wysocki is a meteorologist who specializes in forecasting and weather analysis at the Northeast Regional Climate Center. He says stratospheric warming causes the polar vortex to weaken, which results in arctic air moving south.
“A polar vortex is an upper level low pressure region, located about 60,000 feet above the Earth's poles. It was first described as early as 1853 as a ‘circular gale’ reaching the upper atmosphere. Underneath this vortex, at the surface, lies a large mass of cold, dense arctic air.
“The polar vortex weakens and strengthens from year to year. When the polar vortex of the Arctic is strong — due to stratospheric cooling — there is a single vortex, and the arctic air stays well north of 60 degrees north; when weak — due to stratospheric warming — it will break into two or more vortices; when very weak, the flow of arctic air becomes more disorganized and masses of cold arctic air develop.
“These surface arctic highs move southward during the weak or very weak phase across North America, portions of Europe, and Asia during the winter. The arctic high pressures then move the polar vortex, the polar jet stream, and polar front southward, bringing with it a rapid and large temperature drop known as ‘cold outbreaks’, which occurred in 2014, 1989, 1985, 1982, and 1977 across the northern portions of the United States.”