Aland, where it's located

The climate of the Åland islands is Baltic, that is, moderately continental, with cold winters, during which the average temperature is a few degrees below freezing, and mild to pleasantly warm summers.
The Åland islands lie south-west of Finland, between the Baltic Sea and the Gulf of Bothnia, and have a climate relatively mitigated by the sea. On average, the first snowfalls occur in November, though the ground is permanently snow-covered from the beginning of January to the end of March. The white nights occur from 12 May to 1 August.
The average temperature of the coldest month (February) is of -3.5 °C (26 °F), that of the warmest month (July) is of 16.1 °C (61 °F). The temperature dropped to -32 °C (-25.5 °F) in January 1987, while it reached 31 °C (88 °F) in July 2018. Here are the average temperatures in the capital, Mariehamn.
Mariehamn - Average temperatures
Min (°C)-5-7-40481211740-4
Max (°C)002713172019151052
Min (°F)231925323946545245393225
Max (°F)323236455563686659504136

Precipitation amounts to 610 millimeters (24 inches) per year: so, it is at an intermediate level. It ranges from 30 mm (1.2 in) in the driest months (February, April) to 75 mm (3 in) in the wettest (August). Here is the average precipitation.
Mariehamn - Average precipitation

On average, there are around 1,910 sunshine hours per year. In summer, also due to the length of the days, the sunshine amount is quite good, and definitely better than in Norway. Here are the average sunshine hours per day.
Mariehamn - Sunshine

The sea temperature ranges between 1 °C (34 °F) and 17 °C (63 °F). So, it never becomes warm for swimming. Here are the average sea temperatures.
Mariehamn - Sea temperature
Temp (°C)32136111617151185
Temp (°F)373634374352616359524641


Best Time

The best time to visit the Åland islands is the summer, from June to August, since it is the mildest season. However, you must take into account some rainy days and a bit of cold at night.