Stockholm has a humid continental climate in the 0 °C isotherm and an oceanic climate (Cfb) in the -3 °C isotherm. Although winters are cold, average temperatures generally remain above 0 °C for much of the year. Summers are pleasantly warm, and precipitation occurs throughout the year.
Due to the city’s high northerly latitude, the length of the day varies widely from more than 18 hours around midsummer to only around 6 hours in late December. The nights from late May until mid-July are bright even when cloudy. Stockholm has relatively mild weather compared to other locations at a similar latitude, or even farther south. With an average of just over 1800 hours of sunshine per year, it is also one of the sunniest cities in Northern Europe, receiving more sunshine than Paris, London and a few other major European cities of a more southerly latitude. Because of the urban heat island effect and the prevailing wind traveling overland rather than sea during summer months, Stockholm has the warmest July months of the Nordic capitals. Stockholm has an annual average snow cover between 75 and 100 days.
In spite of its mild climate, Stockholm is located further north than parts of Canada that are above the Arctic tree line at sea level.
Summers average daytime high temperatures of 20–25 °C (68–77 °F) and lows of around 13 °C (55 °F), but temperatures can reach 30 °C (86 °F) on some days. Days above 30 °C (86 °F) occur on average 1.55 days per year (1992–2011). Days between 25 °C (77 °F) and 30 °C (86 °F) are relatively common especially in July and August. Night-time lows of above 20 °C (68 °F) are rare, and hot summer nights vary from 17 to 18 °C (63 to 64 °F). Winters generally bring cloudy weather with the most precipitation falling in December and January (as rain or as snow). The average winter temperatures range from −3 to −1 °C (27 to 30 °F), and occasionally drop below −20 °C (−4 °F) in the outskirts. Spring and autumn are generally cool to mild.
The climate table below presents weather data from the years 1981–2010 although the official Köppen reference period was from 1961 to 1990. According to ongoing measurements, the temperature has increased during the years 1991–2009 as compared with the last series. This increase averages about 1.0 °C (1.8 °F) overall months. Warming is most pronounced during the winter months, with an increase of more than 2.0 °C (3.6 °F) in January. For the 2002–2014 measurements some further increases have been found, although some months such as June have been relatively flat.
The highest temperature ever recorded in Stockholm was 36 °C (97 °F) on 3 July 1811; the lowest was −32 °C (−26 °F) on 20 January 1814. The temperature has not dropped to below −25.1 °C (−13.2 °F) since 10 January 1987.
The warmest month ever recorded was July 2018 with a mean temperature of 22.5 °C (72.5 °F) which is also the nationwide record.
Annual precipitation is 546.4 mm (21.51 in) with around 170 wet days and light to moderate rainfall throughout the year. The precipitation is not uniformly distributed throughout the year. The second half of the year receives 50% more than the first half. Snowfall occurs mainly from December through March. Snowfall may occasionally occur in late October as well as in April.
In Stockholm, the aurora borealis can occasionally be observed.