Budapest has a humid subtropical climate ("Cfa" in Köppen climate classification), with relatively cold winters (near of a humid continental climate when the 0 °C isotherm is used) and warm summers (near of an oceanic climate) according to the 1971–2000 climatological norm. Winter (November until early March) can be cold and the city receives little sunshine. Snowfall is fairly frequent in most years, and nighttime temperatures of are not uncommon between mid-December and mid-February. The spring months (March and April) see variable conditions, with a rapid increase in the average temperature. The weather in late March and in April is often very agreeable during the day and fresh at night. Budapest's long summer – lasting from May until mid-September – is warm or very warm. Sudden heavy showers also occur, particularly in May and June. The autumn in Budapest (mid-September until late October) is characterised by little rain and long sunny days with moderate temperatures. Temperatures often turn abruptly colder in late October or early November.