A cold wave is a stretch of unusually low temperatures that lasts several days or longer. The exact threshold varies by region; what counts as extreme in one climate may be ordinary in another. The key is the departure from local normals and the duration.

These events often follow the southward surge of a strong polar air mass. Clear skies and light winds at night allow rapid radiational cooling, deepening the cold. Wind can make the air feel even colder through wind chill.

Impacts include frozen pipes, stressed livestock, increased heating demand, and health risks for vulnerable people. Warnings typically urge reduced outdoor exposure and protection of infrastructure. In some regions cold waves are associated with specific large-scale patterns such as a negative Arctic Oscillation.

Records of past cold waves help communities set design standards for buildings and power systems.