What is a heat wave? Here's what it is, how it effects your body and how to stay safe.

Excessive heat can strike at any time during the year, even if you live in places where temperatures over 100 degrees are considered the norm. 

Sometimes, the weather can become unbearable. It can feel as if you've stepped into an oven whenever you walk outside. In cases of extreme heat, your body can react in adverse ways, including experiencing dehydration or, worse, heat stroke, according to the Mayo Clinic. 

Throughout history, heat waves have struck various parts of the U.S. from coast-to-coast. The summer of 1936 is one of the hottest on record and impacted the country when air conditioning was not a staple in average homes, according to the National Weather Service. Around 5,000 Americans died from the extreme heat, said the NWS.  

But what is a heat wave, and what causes it? 

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What is a heat wave?

A heat wave is a period of time when temperatures are well above average and much warmer than usual for that area and time of year, said Bianca Feldkircher, lead meteorologist at the National Weather Service in Phoenix.

Heat waves can vary in length and intensity. But, in order to be classified as a heat wave, the high temperatures must last for at least two days, said Feldkircher. 

Heat waves can occur at any time of year and can take place anywhere in the world. As of July 2022, 28 states, extending from California to New Hampshire, are under "excessive heat warnings and heat advisories," according to the National Weather Service. 

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What causes a heat wave?

Heat waves are typically caused by "unusually strong, high pressure systems," said Feldkircher. 

According to the Farmer's Almanac, air from atmospheric upper levels is pulled downward and is then compressed, causing increases in temperature. The longer this high pressure system stays, the hotter the area becomes. 

When these high pressure systems linger over an area for a period of time, it is then classified as a heat wave, Feldkircher said. 

What happens to the human body during a heat wave?

During extreme temperatures and heat waves, people may experience dehydration, heat exhaustion and in the most extreme cases, heat stroke, according to Boston University. 

According to the Centers for Disease Control and Prevention, heat stroke is considered the most serious heat-related illness. Symptoms of heat stroke include: 

• Confusion, altered mental status, slurred speech

• Loss of consciousness

• Hot, dry skin or profuse sweating

• Seizures

• Very high body temperature

Heat stroke can even be fatal if not treated properly. 

Heat exhaustion is the result of excessive loss of water and salt, according to the CDC. Its symptoms include: 

• Headache

• Nausea

• Dizziness

• Weakness

• Irritability

• Thirst

• Sweating

• Higher body temperature

• Decreased urine output

Those most at risk during heat waves include the elderly, children, those who are pregnant and those who are homeless, said Feldkircher. 

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How do you stay safe in heat wave?

Unusually high temperatures should be taken extremely seriously, said Feldkircher. There are various ways to stay safe in a heat wave. 

It is important to limit any kind of outdoor activity during the hottest parts of the day, said Feldkircher. If you can avoid going outdoors during those times, try to put off activities until the morning or after the sun goes down.

Staying hydrated is also key to staying safe in heat waves. According to the Red Cross, on average, a person should drink approximately 3/4 of a gallon of liquids per day.

Eating foods that have a high water content, such as fruits and vegetables, can also keep you hydrated, said Feldkircher.

The Red Cross also advises to keep your home cool by doing the following: 

• Covering windows with drapes or shades. 

• Installing air conditioners and insulation around them.

• Use window reflectors to send heat back outside. 

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This article originally appeared on USA TODAY: Heat wave 2022: What causes a heat wave and how you can stay safe