Cold Wave

A cold wave is a rapid fall in atmospheric temperature that, in the definition used by the United States National Weather Service, occurs within a 24-hour period and requires substantially increased protection for agriculture, industry, commerce, and social activity; in the United States a cold spell is marked by the national average high temperature dropping below 20 degrees Fahrenheit, about minus 7 degrees Celsius, and a particularly severe or prolonged one may be classed as a cold air outbreak. Cold waves raise mortality worldwide, with temperature-related deaths during cold periods often exceeding those from heat waves, especially in less developed regions, and grazing animals can die of hypothermia or starvation when cold combines with heavy snow. They can freeze uninsulated water pipes and plumbing, strain or fail power generation including hydroelectric systems just as demand for heat and fuel surges, and disable vehicles when antifreeze or batteries fail. For agriculture the effect can be severe, since an unexpected freeze during the growing season, especially in subtropical regions, can destroy crops outright, and the resulting dead plant matter can later raise wildfire risk.