Need a conversation starter? When in London, you can always rely on the weather for that. Never the same from start to finish, days spent in London can be filled with heat, rain and wind. That being said, the warmest months lie between June and September, with average temperatures ranging between 15 and 18 degrees C. The coolest periods range between December to March, with 5 to 7 degrees C as the average. Rain is possible, sunburns are possible. Be prepared for it all when visiting England's capital.