A Chilly Start to 2018

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The U.S. has started 2018 with record low temperatures. Sometimes winter weather is affected by an low-pressure area over the North Pole called the polar vortex. In 2014 especially cold temperatures in U.S. cities like Chicago, above, were blamed on this phenomena.

The U.S. has started 2018 with record low temperatures. Sometimes winter weather is affected by changes in a low-pressure area over the North Pole called a polar vortex. In 2014, especially cold temperatures in U.S. cities like Chicago, above, were blamed on this phenomenon.

It’s cold—very cold. As 2018 begins, the United States is experiencing record cold weather. On New Year’s Day, Aberdeen, South Dakota, reported a record low temperature of 32 degrees below zero. In Des Moines, Iowa, the weather was so cold local officials closed a downtown ice-skating rink until temperatures rose above zero.

Southern states were affected as well. On January 2, temperatures in Atlanta, Georgia, dropped to an unusually cold 14 degrees, while temperatures in Mobile, Alabama, fell to 20 degrees. Special warming shelters were opened over much of Mississippi, Louisiana, and Alabama.

Wind Chill

One of the dangers of winter storms is called wind chill. Wind chill is the effect that cold air has on people and animals.

When cold air flows over skin, the body loses heat. Wind chill is determined by the rate at which bodies lose heat when exposed to the cold. When heat leaves your body, it can make a chilly temperature feel even colder than it actually is. For example, when the temperature is zero and there is a 15 mile-per-hour wind, the wind chill is calculated to be -19 degrees. At that temperature, exposed skin can freeze in just a few minutes.

Wind chill can lead to two medical problems: hypothermia and frostbite.

Hypothermia occurs when the body’s normal temperature of 98.6 degrees falls below 95 degrees. Hypothermia is not limited to winter, however. Even during the summer, if you spend too much time in water as warm as 60 degrees without a wetsuit, hypothermia may occur. According to the National Institute of Aging, 28,000 people die from hypothermia each year. Older people are more susceptible to hypothermia than younger people.

Frostbite results when the body tries to protect itself during extremely cold weather. In order to keep vital organs, such as the heart or lungs, functioning, the body cuts off circulation to less vital parts, such as the feet, hands, nose, and other extremities. Without blood circulating in them, these body parts can eventually freeze. The first signs of frostbite are a tickling feeling in the affected area and cold skin. Ice crystals form on the skin. From there, frostbite can lead to skin turning blue or black. There are four stages of frostbite. The first degree is the mildest form, when the surface of the skin freezes. By the second degree, the skin will actually feel warm, even though it has not defrosted. Once defrosted, the skin will have blisters that can last up to three days. At the next stage, the skin turns pale, white, or red. By the time a person has fourth degree frostbite, the skin and tissue underneath are frozen. The tissue can die, and at this point the affected body part will feel numb. The skin will turn blue or black. When rewarmed, there is usually a lot of pain.

How can you stay safe this winter? Be sure to dress in layers. Layers of thinner clothes will keep you warmer than a single thick layer. Don’t forget to protect your head with a hat, your neck with a scarf, or your hands with gloves. Eat nutritious foods and drink plenty of warm drinks. If you have a friend or relative who lives alone, be sure to check on him or her daily to make sure that he or she is safe.

Wind can make already cold temperatures seem even colder. The wind chill is determined by the rate at which the human body loses heat under cold conditions. This chart shows how low temperatures combined with wind can make the temperature feel even colder then it actually is. wind work together to make As you move from left to right in the chart, the possibility of frostbite increases.

Wind can make already cold temperatures feel even colder. Wind chill is based on the rate at which the human body loses heat under cold conditions. As temperatures drop and wind speeds increase, wind chills increase.Wind chill can cause frostbite, so it is important to cover skin the colder it gets.

Meteorologists and Pressure Systems

Meteorologists are scientists who study weather. Whenever they say a temperature is higher or lower than normal, they are comparing the current temperature to temperature readings collected over a set period of time. In order to determine what constitutes normal weather for an area, scientists examine the temperature, precipitation, and wind over a thirty-year period. Currently, meteorologists use the 30-year period from 1981 to 2010. In 2021, meteorologists must determine a new set of normal temperatures. These will be based on the weather from 1991 to 2021.

Scientists attribute storms to changes in air pressure. Although we do not feel it, air is not weightless. The force of air pressing down on an area is called air pressure. Normally, the air in Earth’s atmosphere presses down on our skin with a force of about 15 pounds per square inch.

However, air pressure can vary. In some circumstances, the weight of air is greater than at other instances. For example, the air is more dense and therefore heavier in a high-pressure system. Areas where the air is less dense and the weight lower are called low-pressure systems. When high and low pressure systems meet, both systems are affected. The low pressure system pulls in extra air from the high pressure system.

When a high- and low-pressure system meet, the air drains from the high-pressure area into the low-pressure area. Once inside the low-pressure system, the higher-pressure air travels upward to where the air is less dense. People experience this process as wind and storms. The greater the difference in pressure between the high- and low-pressure systems, the stronger the wind will be.

How can you tell whether you are inside a high-pressure system? If the weather is sunny and clear, you are likely in a high-pressure system. If the weather is windy and stormy, you are probably in a low-pressure system.

The Polar Vortex

Sometimes especially chilly winter weather is caused by the polar vortex. A vortex is another word for whirlpoolWithin a whirlpool, water travels rapidly in a circle, which causes a small depression in its center. Wind in a polar vortex also moves in a circle around a center point. Earth has two polar vortexes, one at the South Pole and the other at the North Pole. The Arctic polar vortex can affect weather in the United States and elsewhere in the Northern Hemisphere.

The polar vortex affects the polar jet stream, which can cause changes in U.S. weather. The polar jet stream is a river of wind that flows around seven miles above Earth’s surface. The polar jet stream keeps colder air north and warmer south. The polar jet stream forms between 50 and 60 degrees north latitude. To the south, it starts just north of the Canadian city of Vancouver, and ends around the small town of Wainwright, Alaska, in the north. The polar vortex starts about 10 miles above the Arctic and continues to about 50 miles up. Jet stream winds blow anywhere from 120 to 250 miles per hour. The polar vortex ensures that the polar jet stream travels around the globe in a mostly circular path. Because the polar vortex is located so high above Earth’s surface, you cannot feel it directly.

“It’s not a surface feature,” explains Lynn Harvey, an atmospheric scientist from the University of Colorado, Boulder. “You’re never going to be in it unless you’re in a spy plane. Even then, you’d never know it, because it’s invisible.”

Sometimes the polar vortex can move beyond its usual boundaries. If the vortex weakens, the jet stream may wobble and be pushed to the south by an area of high pressure. A section of the polar vortex can break off from the rest and travel south, pulled by the wandering jet stream. The polar vortex causes the dividing line between colder and warmer weather to move more southerly than is normal. When this happens, temperatures even in usually mild areas can suddenly fall.

Not all winter weather is caused by the polar vortex, however. Lynn Harvey thinks the term is heard so often because it sounds scary to most people. It is often used in the news and gets people’s attention. “Just the word vortex is frightening,” she says. “It hits us at our core.”

Additional Resources

Read more about the recent wave of cold temperatures in the U.S. at National Geographic and CNBC.

Learn more about polar vortexes at SciJinks  and NASA.

Discover more about weather at the National Weather Service and the United States Search and Rescue Task Force.

Images and Sources

Chicago skyline photo: Edward Stojakovic
Chicago skyline photo license: Creative Commons 2.0

Wind chill chart: National Weather Service
Wind chill chart license: pubic domain