What Is a Heat Wave?

The Short Answer

A heat wave is a period of unusually hot weather that typically lasts two or more days. To be considered a heat wave, the temperatures have to be outside the historical averages for a given area.

Dangerous Heat

For some, a heat wave might sound like an excuse to run around with a hose or into some sprinklers. In reality, though, heat waves are no laughing matter. They are serious weather phenomena that can be quite dangerous.

You see, there’s hot and then there’s HOT. One example of a HOT time was in late June and early July 2012 in the United States. During that time period, more than 8,000 warm temperature records were broken or tied. Many of these records had been unchallenged since the 1930s. Roads actually buckled in Chicago. Many deaths were attributed to the heat nationwide.

How Do Heat Waves Form?

Heat waves are generally the result of trapped air. During the 2012 heat wave, air was trapped above much of North America for a long period of time. As opposed to cycling around the globe, it simply stayed put and warmed like the air inside an oven.

The culprit? A high-pressure system from Mexico. Between June 20th and June 23rd, this system migrated north. It grew in size, and it parked itself over the Great Plains of the United States.

High-pressure systems force air downward. This force prevents air near the ground from rising. The sinking air acts like a cap. It traps warm ground air in place. Without rising air, there was no rain, and nothing to prevent the hot air from getting hotter.

But that wasn’t all. A weather pattern that normally pulls air toward the east was also weaker at the time. That meant that there was little that could be done to push this high-pressure cap out of the way.

Heat Wave Safety

Heat waves like this may be less exciting or dramatic than other natural disasters like tornados, hurricanes, flooding, or even thunderstorms, but heat waves kill more people in the United States than all other weather-related disasters combined.

Check out the sidebar to learn more about what you can do to stay safe!

A heat wave is simply a period of unusually hot weather that typically lasts two or more days. The temperatures have to be outside the historical averages for a given area. A couple of 95 degree summer days in Maine, for example, might be considered a heat wave, but a couple of 95 degree summer days in Death Valley would be pretty unremarkable.

• Take it easy. Slow down and avoid doing strenuous work.
• Dress for the weather. Wear lightweight, light colored clothing.
• Avoid high-protein foods and meat. Eating these can increase your body’s heat production.
• Drink lots of water. Unless you have a condition that is affected by changing how much fluid you drink, it’s a good idea to keep as hydrated as possible.
• Find an air-conditioned place to hang out. Don’t have an air conditioner of your own? Find a friend with one, or go to a public place like a library that has one.
• Avoid getting too much sun. Sunburns make it harder for your body to cool off.
• Be very careful in cars. Cars heat up extremely fast. You should never spend time in a parked car with windows closed, and you should always be wary of hot metal objects both inside (like seatbelt buckles) and outside the car.