On average, only one in three days will bring rain and usually then only for a short period. In some cases, 2010 being a well-known example, the city can go without rain for several weeks, leading to hosepipe bans across the city.

As for temperatures, London is far milder than nearby continental European cities due to the presence of the Gulf Stream. The average daily maximum is 8°C (46°F) in December and January (a full 4 degrees warmer than the rest of the United Kingdom on long-term average) and February is usually the coldest month of the year. In summer, temperatures can rise up to 24°C (75°F), and once reached as high as 38°C (100°F), as happened in 2003.

Due to the urban microclimate, inner London can feel hot and humid for several days in the summer months, especially during the evenings. However, summer is still perhaps the best season for tourists as it has long daylight hours as well as mostly mild temperatures.

Snow does occur, usually for a few days at the beginning of the year. In recent years, 2012 had snow both in February and December, with more in January 2013.

When it does appear, it causes huge transport problems. In 2010, just 7 cm (3 in) of snow caused trains to stop running, airports to see significant delays, and mail service problems, and this is a fairly typical response to even minor icy conditions.

Although roads will be gritted, it can be very dangerous in London in the snow, as slippery conditions combine with crowds with inevitable consequences. So travellers should be very prepared for problems in the snow, both in moving by foot and public transport. On the other hand, London does look uniquely beautiful in the snow, with the landmarks and parks taking on a postcard-perfect air.

Although the average day is mild and clear, rain, winds, sun or snow could come very quickly. So pack clothes accordingly.