Xi'an has a temperate, semi-arid climate (Köppen BSk) influenced by the East Asian monsoon. The Wei River valley is characterised by hot, humid summers and cold, dry winters. Spring and autumn are somewhat brief and dry. Xi'an receives most of its annual precipitation from August to late October in the form of rain. Snow occasionally falls in winter but rarely settles for long. Dust storms often occur during March and April as the city rapidly warms up. Summer months also experience frequent but short thunderstorms. Monthly mean temperatures range from around the freezing mark in January to 26.6 °C (79.9 °F) in July, with an annual average of 13.7 °C (56.7 °F). Extreme temperatures have ranged from −20.6 °C (−5 °F) to 42.9 °C (109 °F)
