Oslo has a humid continental climate (Köppen climate classification: ''Dfb'') or, if the original Köppen winter threshold  is used, an oceanic climate (''Cfb'') in the 1991-2020 base period. Oslo has pleasantly warm summers and fairly cold winters. Oslo has a significant amount of rainfall during the year. This is true even for the driest month. The driest season is winter and spring, and the wettest is summer and autumn. Because of the city's northern latitude, daylight varies greatly, from more than 18 hours in midsummer, when it never gets completely dark at night (no darker than nautical twilight), to around 6 hours in midwinter. 