Summer is when London comes into its own — Victoria Park fills with weekend festivals, the Old North porches fill with students, baseball games run at Labatt Park, and the patios on Richmond Row open up. July is festival month: the Home County folk festival, Sunfest world music, Rock the Park on the Thames.
Autumn is shorter and beautiful — late September through mid-October the maples along the river turn red. Winter is grey, cold, and very long; January temperatures sit between -10 and -5°C and snow lies until March. Spring is brief and muddy. If you have one weekend, take the second weekend of July.