What Causes a Heat Wave?

The Farmers’ Almanac is calling for hotter-than-normal conditions for many regions of the U.S. and Canada this summer. The unseasonably warm weather some areas saw early last week was just a foretaste of what may be in store over the coming months. Depending on how you feel about heat, that may or may not be welcome news.

But what causes a heat wave, anyway? Why can we have a wet, chilly summer one year and a sizzler the next? Or even between one week and the next?

A heat wave occurs when a system of high atmospheric pressure moves into an area. In such a high-pressure system, air from upper levels of our atmosphere is pulled toward the ground, where it becomes compressed and increases in temperature.

This high concentration of pressure makes it difficult for other weather systems to move into the area, which is why a heat wave can last for several days or weeks. The longer the system stays in an area, the hotter the area becomes. The high-pressure inhibits winds, making them faint to nonexistent. Because the high-pressure system also prevents clouds from entering the region, sunlight can become punishing, heating up the system even more. The combination of all of these factors come together to create the exceptionally hot temperatures we call a heat wave.

While the phrase “dangerous weather” may conjure up images of blizzards, hurricanes or tornadoes, it’s important to remember that heat waves can be deadly. During a heat wave, you can protect yourself by staying out of the sun during the hottest parts of the day, avoiding strenuous activities, and keeping yourself hydrated with plenty of fresh water.