Typical weather ranges from 3 - 8° C (38 - 46° F) in the depths of winter, to sunny days of 25 - 30° C (77 - 86° F) in the summer.
Convert to Fahrenheit or from Fahrenheit.
Spring and autumn are pleasant, but can be fairly wet at times. However, the weather is certainly not as bad as its reputation around the world suggests.
The last smog or "peasouper", by the way, was during 5th - 9th December 1952. The best time to visit, weatherwise, is May to September.