A cold wave is defined as at least 3 consecutive days with temperatures significantly below the climatic average. AEMET declares one when minimum temperatures are extremely low across a wide area.
Causes
They are caused by polar or Arctic air intrusions toward mid-latitudes, usually linked to weakening of the polar vortex or southward displacement of the jet stream. In Spain, the most severe cold waves bring snowfall at low elevations, widespread frost, and sub-zero temperatures even on the coast. Health risks (hypothermia) and agricultural damage (frost) are considerable.