Diemen has an oceanic climate with mild winters and equally mild summers leaning on the cooler side.
Winter: Winter lasts from December to February and is accompanied by heavy snowfall.
Spring: The months of March and April are accompanied by an increase in temperature and the weather is cool and pleasant.
Summer: Beginning in June and lasting till August, summers in Diemen are warm and crowded.
Autumn: The weather starts getting a little cold during this period and the mercury is around 13 degree Celsius.
The best time to visit Diemen is probably during the Summers, but then you have to be prepared for a lot of rush and thick crowds. Going in Spring is also ideal as the weather is pleasant during this time, though a little on the colder side.