Quebec has three main climate regions. Southern and western Quebec, including most of the major population centres, have a humid continental climate (Koppen climate classification Dfb) with warm, humid summers and long, cold winters. The main climatic influences are from western and northern Canada which move eastward and from the southern and central United States that move northward. Because of the influence of both storm systems from the core of North America and the Atlantic Ocean, precipitation is abundant throughout the year, with most areas receiving more than 100 centimetres(40 in) of precipitation, including over 300 centimetres (120 in) of snow in many areas. During the summer, severe weather patterns (such as tornadoes and severe thunderstorms) occasionally occur.