What is a prolonged period of unusually hot weather called?

What is a prolonged period of unusually hot weather called? A heat wave is the answer. It is a period of abnormally hot weather lasting multiple days, usually judged against the normal climate and season for a particular location.

There is no single temperature that defines a heat wave everywhere. A temperature considered ordinary in a hot desert may be dangerous and exceptional in a cooler region. Meteorological definitions may use unusually high daytime temperatures, warm nights, humidity, or a combination of thresholds over consecutive days. In the United States, regional definitions often differ; some areas use three or more days around 90°F, while others rely on heat-index values.

Heat waves are hazardous because the body may struggle to cool itself, especially during hot nights when recovery is limited. Older adults, infants, outdoor workers, and people with certain health conditions face greater risk. A heat wave is not the same as drought: drought is a prolonged lack of precipitation, whereas a heat wave is defined by exceptional heat, though the two can occur together.