Heat wave

Temperature difference in Europe from the average during a heat wave in 2003.

A heat wave is a period of unusually warm or very hot weather, and may be accompanied by high humidity. "Heat wave" is not an exact term:^[1] Any weather that feels warmer than people expect, might be called a heat wave. For example, temperatures normal for a warmer climate might be called a "heat wave" by people living in a place that is usually cooler.^[2] So a "heat wave" could mean a little warm weather, (like "several days as hot as summer, but in winter"), or temperatures so high they make history, (such as, "the hottest summer in a hundred years").

Heat Wave Media

A high pressure system in the upper atmosphere traps heat near the ground, forming a heat wave (for North America in this example)
Scorched grass in Greenwich Park, London, England, during a heatwave in August 2022.
Map of increasing heat wave trends (frequency and cumulative intensity) over the midlatitudes and Europe, July–August 1979–2020
Heat stroke treatment at Baton Rouge during the 2016 Louisiana floods
The National Weather Service risk categories for NWS HeatRisk
2009 southeastern Australia heat wave, thermal map approximate affected area shown in red