The climate of Sundsvall is cold continental, with very cold winters, during which the temperature is often below freezing, and mild summers.
The city is located in central Sweden, on the Gulf of Bothnia coast. During the coldest winters, the temperature can go down to -32/-34 °C (-26/-29 °F). In summer, it can touch or exceed 30 °C (86 °F), although rarely.
The average temperature of the coldest month (January) is of -6.6 °C (20 °F), that of the warmest month (July) is of 16.7 °C (62 °F). Here are the average temperatures.
Sundsvall - Average temperatures
Min (°C)-11-10-6-237121160-3-8
Max (°C)-2-138141822201582-1
Min (°F)121421283745545243322718
Max (°F)283037465764726859463630

Precipitation amounts to 540 millimeters (21.3 inches) per year: so, it is at an intermediate level. It ranges from 30 mm (1.2 in) in the driest months (February, March, April) to 65 mm (2.6 in) in the wettest ones (August, September). Here is the average precipitation.
Sundsvall - Average precipitation

On average, there are around 1,805 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.
Sundsvall - Sunshine

The sea temperature ranges between 1 °C (34 °F) and 16 °C (61 °F). So, it never becomes warm for swimming. Here are the average sea temperatures.
Sundsvall - Sea temperature
Temp (°C)211249151613953
Temp (°F)363434363948596155484137


Best Time

The best time to visit Sundsvall 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.