The freezing level is the 0 °C isotherm in the free atmosphere. Above this altitude, precipitation falls as snow; below, it melts to rain. However, the actual snow line is usually 200–400 m below the freezing level because flakes need a cold-air path to melt.
In Spain
The freezing level varies from 500–1,000 m during cold winter intrusions to 3,500–4,500 m in summer. Snowfall in cities like Madrid (650 m) requires a freezing level below ~1,000 m, only occurring with polar or Arctic air masses. Numerical models (GFS, ECMWF) predict this altitude accurately.