The climate of Zagreb is classified as an oceanic climate (Köppen climate classification ''Cfb''), but with significant continental influences and very closely bordering on a humid continental climate (''Dfb'') as well as a humid subtropical climate (''Cfa''). Zagreb has four separate seasons. Summers are generally warm, sometimes hot. In late May it gets significantly warmer, temperatures start rising and it is often very warm or even hot with frequent afternoon and evening thunderstorms. Heatwaves can occur but are short-lived. Temperatures rise above  on an average 14.6 days each summer. Rainfall is abundant in the summertime and it continues to be in autumn as well. With 840 mm of precipitation per year, Zagreb is Europe's ninth wettest capital, receiving less precipitation than Luxembourg but more than Brussels, Paris or London. Autumn in its early stage often brings pleasant and sunny weather with occasional episodes of rain later in the season. Late autumn is characterized by an increase in rainy days as well as by steadily declining temperature averages. Morning fog is common from mid-October to January, with northern city districts at the foothills of the Medvednica mountain as well as the districts along the Sava river being more prone to all-day fog accumulation. Winters are relatively cold with a precipitation decrease pattern. February is the driest month, averaging 39 mm of precipitation. On average there are 29 days with snowfall, with the first snow usually falling in early December. However, in recent years, the number of days with snowfall has decreased sharply. Springs are generally mild and very pleasant with frequent weather changes and are windier than other seasons. Sometimes cold spells can occur, mostly in their early stages. The average daily mean temperature in the winter is around  (from December to February) and the average temperature in the summer is .