Windermere is set in the Lake District, which is one of the rainiest areas in the United Kingdom. The best weather is usually during June, July, and August, which is when most of the festivals take place. But summertime is also the “high season,” when the area is flooded with visitors. So expect large crowds and limited parking.  Or, consider bringing rain gear and traveling during the spring or fall, when rates drop significantly. During the winter you may have the area to yourself, but many of the attractions close due to snow.