 That humidity persists for the entire year because of precipitation brought on by cyclones originating in the Mediterranean or in the Russian north.That precipitation itself remains in the Po Valley because of its poor ventilation.Data from the indicates that, based on the more than thirty years (1961–1990) of reference accumulated by the World Meteorological Organization, that the average temperature of the Milan area the coldest month, January, is and that of the hottest month, July, is .