What Is a Polar Vortex Weather System?

01Weather experts say extreme cold in many parts of the United States this winter has been driven by a polar vortex.

02But what is this weather system and how does it work?

03The National Oceanic and Atmospheric Administration, NOAA, describes a polar vortex as strong westerly winds that form each winter in the atmosphere above the North Pole.

04These cold winds move about 16 to 48 kilometers above the surface in the Arctic area in the part of the atmosphere called the stratosphere.

05At times, the polar vortex can weaken, causing masses of cold air to break off and move south.

06A polar vortex can also push warmer air in northerly directions.

07The Associated Press, AP, reports that several vortex events have affected parts of the U.S.

08this winter.

09Experts say weather forces in the Arctic have combined to push colder air to the U.S.

10and Europe.

11Temperature readings that take into account the effects of wind, called windchill readings, fell to minus 51 degrees Celsius in parts of the U.S.

12Midwest.

13Meteorologists say windchill readings are colder than air temperature readings.

14The U.S.

15National Weather Service, NWS, warned people in affected areas that such low temperatures can cause frostbite and hypothermia if skin is not protected from the cold.

16Weather officials also warned that long-term cold temperatures can cause water pipes in or around homes to freeze and burst.

17The NWS noted that almost every U.S.

18state, except for Hawaii, California, and Florida, is expected to report low windchill temperatures.

19The coldest temperatures were expected in the Midwestern states of Kansas, Nebraska, and Missouri.

20In an explanation on its website, NOAA states that the polar vortex always surrounds both of Earth's poles.

21The systems strengthen in the winter and weaken in the summer.

22Every year or so, the polar vortex becomes weaker.

23This can cause the system to be pushed off the pole or split into two.

24This can lead to cold air at the surface being pushed southward and warm air being pushed to the north.

25NOAA says its weather models are predicting low temperatures for states including Oklahoma, Colorado, Nebraska, Missouri, Illinois, and Iowa.

26Other states likely to have very low temperatures are Wyoming, Montana, North Dakota, South Dakota, Minnesota, Wisconsin, and Michigan.

27The agency said some storms could bring heavy snow or flooding during that time.

28I'm Brian Lynn.

29I'm Brian Lynn.