London's weather is famously unpredictable — bring a light waterproof jacket regardless of season. Summers (June–August) are pleasantly warm at 18–23°C with long daylight hours (sunset at 9pm in June). Winters (December–February) are grey and damp at 4–8°C but rarely below freezing. Snow is unusual and causes considerable disruption when it occurs.
The best weather windows are May–June and September–October: comfortable temperatures, manageable crowds, and good daylight hours. July–August is peak tourist season with maximum prices. Autumn foliage in Hyde Park and Richmond Park is beautiful in October. December's Christmas lights on Oxford Street and Regent Street, and the South Bank Christmas Market, make it a worthwhile winter visit.