Polar Vortex Breaks Down Earlier Than Ever Recorded, Scientists Say

Scientists say the polar vortex, the system of winds that normally holds Arctic air near the North Pole, has broken down earlier than at any time on record, according to a report from AOL. The breakdown could let frigid air spill south over the coming weeks.

That raises a question for the winter outlook. Forecasters had been expecting a warmer winter because of a strong El Niño, and the vortex change could cut against that. Forecasters say it is too early to know which pattern will win out.

Cold is already in the eastern U.S.

Parts of the eastern United States are already running 7 to 14 degrees below average, AOL reported. That is a sizable gap from normal for a region that El Niño winters tend to leave milder.

What the polar vortex is

The polar vortex is a regular feature of the polar regions: a mass of cold air and low pressure that usually stays fairly close to the north and south poles. When the vortex weakens or breaks down, the cold air it was holding in place can move toward lower latitudes. For a longer explanation of how that process sends cold air toward populated areas, see this overview of the polar vortex and Arctic cold outbreaks.

What El Niño usually does to winter

El Niño is part of a climate cycle in which water in the equatorial Pacific Ocean becomes warmer than average. Sea surface temperatures in the region where El Niño develops are expected to be 2.5 degrees Celsius above normal in what forecasters have been calling a historically strong event.

Historically, El Niño brings wetter conditions to the southern U.S. and drier weather to the North. It also tends to produce milder winters across much of the country. In the Atlantic, it strengthens upper-level winds, which makes it harder for hurricanes to form.

Why it matters

The two forces point in opposite directions. A strong El Niño favors a milder winter across much of the country, while a vortex that has already broken down can let Arctic air move south. Which one dominates will shape the winter weather people in affected areas see. Forecasters told AOL it is too early to say.

A separate El Niño concern

AOL also linked to a study that says a super-sized El Niño could cause more than 450,000 heat deaths by February. That finding concerns heat, not the winter cold now affecting the eastern U.S., and it comes from a different piece of research than the vortex report.

Where to follow conditions

Readers who want current conditions for their area should follow official warnings and forecasts from the National Weather Service or the Met Office, along with local authorities.

Source: AOL