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Weather Overview for London

London has a temperate maritime climate with all four seasons and no extremes of temperature. However, it has a microclimate knows as an ‘urban heat island’. The mass of heated buildings and people result in temperatures that are a couple of degrees warmer than outside of the city. As a result, London is one the warmest places in the UK.

Contrary to popular belief, the average annual rainfall in London is not particularly high – Sydney, for example has higher annual rainfall. It’s just that there are a high number of those grey drizzly days… Total rainfall may not be that high, but the number of ‘rainy days’ is.

Weather can vary greatly from year to year; you might get a particularly cold winter, or a particularly wet summer, or a very hot one. That’s the thing: if you come to visit London you just don’t quite know what you’re going to get. Day to day and moment to moment conditions are also highly changeable and hard to predict.

Summer weather: June – Mid September

The best way to describe a London summer is unpredictable. You should be prepared for all eventualities. You could get a week of continuous rain or, just as likely, a week of glorious sunshine and temperatures in the high 20s. It’s true that a good summer’s day in London is hard to beat, but this good summer weather is notoriously unreliable. Perhaps this unpredictability explains why the weather is such a favoured topic of conversation in England.

The average high temperature peaks in summer – July and August - are a favourable 22°C. Some days can see temperatures rise up to and above 30°C during a fine spell of weather. Similarly a July day in the mid-teens is not unheard of. The average low temperature in peak summer is 13°C. Summer 2007 was a particularly bad summer with lots of rain and grey skies. 2003, on the other hand, was one of the hottest summers in recent memory with a record temperature of 38°C. 2009 is set to see yet another heat wave with record highs.

Rainfall in summer is around 50 to 60mm per month, making it very marginally the driest time of year. Expect some rain if you’re in town, though you may escape. Late summer can see evening thunderstorms and short heavy downpours – at least this gets the rain out of the way quickly rather than with the endless drizzle that can occur at other times.

Autumn Weather: Mid September - November

Early autumn, from late September, can see good weather and pleasant temperatures though by October things are start to cool and rainfall increases slightly. The wintry weather begins to appear and November sees the first frosts of winter.

September enjoys average daily highs of 19°C and can still get sunny days in the 20s. Mid to high teens can be possible in October, but by November the temperature will not get far into double figures at its peak.

Autumn is definitely a season of change as the long warm sunny days give way to cooler temperature. The days begin to shorten noticeably.

Late autumn is statistically the wettest time of year in London, though in reality you’re just as likely to get rain at any time of year.

Winter weather: December - February

Winters in London are cold, without being very cold. Generally, the last few winters have been milder than average and as climate change progresses some bizarre weather is being thrown into the mix. In January (2009) London was as stricken as the rest of the country by heavy snowfall, which is rare across the country.

Frosts and snow are rarer in the city than elsewhere due to the ‘urban heat island’ phenomenon. The warmer temperatures mean that if it does fall it less likely for snow to settle than in other parts of the country. The average temperature in the winter is 5°C, with highs averaging 7°C and lows 2°C. It can often drop to 0°C, but temperatures far below are not common, especially in the more built up areas of the city.

A crisp, sunny winter’s day is very beautiful, especially if you find a leafy area. But unfortunately there are a lot of damp, grey days during an English winter. Sunshine levels drop to one hour per day in December and only increase slightly thereafter.

Rainfall is at its highest in late autumn and winter, at between 70 to 80mm per month. This tends to fall as an irritating drizzle so there are a lot of rainy days. Coupled with the short hours of daylight, this can make winter a bit of a grim time – when you’re out in town you may be tempted to duck into the nearest pub and sip ale by the fireplace.

Spring Weather: March - May

Spring, again, is a time of unpredictable weather. Sometimes it can be sunny and a pleasant 20°C while all around is blooming, the birds are chirping and the days getting longer. Other times it can be chilly, grey and damp.

Early spring stills sees a few frosts (though less so in the city), while by late spring you can really start to feel the arrival of summer weather.

March has average highs of just 10°C, while this rises to 17°C by May.

Rainfall is around 50 to 60mm per month in spring. This time is known for its frequent but brief showers – coined the ‘April showers’.

Sunshine levels increase as the season progresses.

Although the UK is not particularly well known for its extreme weather there have been a number of significant weather events affecting London over the years.

 

January 1928 saw the last major flood of London’s city-centre. Heavy snowfalls over the Christmas of 1927 were followed by a rise in temperature and a period of unusually heavy rain in early January 1928. The resulting thaw of the snow combined with the heavy rain resulted in an overall doubling of the amount of water in the river Thames. This coincided with a high spring tide and a storm surge caused by a depression over the North Sea that raised the water level in the Thames Estuary by 1.5 metres.

 

This combination of weather resulted in the highest water levels ever recorded in London. The embankments overflowed and large areas of the city were flooded, including the Houses of Parliament, the Tate Gallery and riverside Underground stations. Again in 1953 a storm surge in the North Sea raised water levels to such an extent that the embankments came within millimetres of overflowing again. To guard against subsequent flooding the Thames Barrier was built as a defence against high tides and storm surges.

 

The Great Smog of December 1952 was the worst air pollution incident in UK history. An anticyclone settled over London causing cold stagnant air to be trapped under a layer of warm air. Unprecedented levels of pollutants such as chimney smoke, particles from vehicle exhausts and sulphur dioxide combined in the windless conditions to produce a thick fog that persisted for 4 days. The ‘peasouper’ - as they were known due to their characteristic yellow-black colour caused by soot particles - cut visibility to just a few metres, meaning driving became impossible. The smog even penetrated indoors causing the cancellation of film screenings and concerts.

 

Londoners were so used to the smog that initially people were not worried about the pollution but it is estimated that 12,000 people died in the following weeks and months due to lung and respiratory tract infections. This event led to an increased awareness of air pollution and efforts were made to improve the air quality in subsequent years and thankfully London’s famous ‘peasoupers’ are now consigned to history.

 

The Great Storm of October 1987 caused 18 deaths as an unusually strong weather system passed over the south of England. In London many trees were blown over causing damage to buildings and flattening parked cars. Six of the seven famous oak trees in Sevenoaks were toppled. Fatalities were kept to a minimum as the storm hit during the night, however this wasn’t the case 3 years later when 97 people were killed in a storm of comparable intensity struck during the daylight hours.

 

In 2006 a tornado struck the NW London area of Kensal Green. £10 million of damage was caused to 100 homes. The UK actually experiences approximately 35-40 tornados a year, which is the highest number of any country in Europe.

 

February 2009 saw the highest UK snowfall for 18 years. London received 20 centimetres of snow. Many airports were closed for a period, public transport was severely affected and much of London’s sporting schedule was disrupted. Hospitals received an increased number of injured patients from slips and falls in the snow and schools were closed for several days.