Oslo has a humid continental climate with warm summers and cold winters. Due to oceanic influences, winters are less cold than more continental areas at same latitude, but still cold enough to be continental. Oslo has a significant amount of rainfall during the year. This is true even for the driest month. 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. Oslo sits right on the border between hardiness zones 7a and 7b.
May 2018 saw hotter than average temperatures throughout the month.
On 30 May 2018, the city saw temperatures rise to 31.1 °C (88.0 °F), making it the hottest May temperature on Oslo records. On 27 July 2018, the temperature in Oslo rose to 34.6 °C (94.3 °F), the hottest ever recorded since 1937, when the weather observations for Oslo have been conducted in the university area at Blindern. However, the warmest temperature ever recorded in the city of Oslo was 35 °C (95 °F) in July 1901. In January, three out of four days are below freezing (0 °C [32 °F]), on average one out of four days is colder than −10 °C (14 °F). The coldest temperature recorded is −29.6 °C (−21.3 °F), on 21 January 1841, while the coldest ever recorded at Blindern is −26 °C (−14.8 °F) in January 1941.