London: time, weather and climate

London's weather is mild and changeable rather than extreme: cool, grey winters, pleasant summers and light rain that can turn up in any month. Its clock is the one the rest of the world is measured against. London keeps Greenwich Mean Time in winter and moves an hour ahead to British Summer Time from late March to late October.

Climate overview

London has a temperate oceanic climate (Köppen Cfb), shaped by the Atlantic Ocean and the warm waters of the North Atlantic Drift. The result is a city without real extremes. Average highs run from 9°C in January to 24°C in July, and average lows from 4°C in the depths of winter to 15°C at the height of summer. The city's urban heat island also keeps central London a little warmer than the surrounding countryside, especially at night.

London's yearly rainfall of 615 mm is lower than that of many cities with a sunnier reputation; Rome, for example, averages 920 mm. What visitors notice is how often it rains rather than how much: there are about 114 days a year with measurable rain, roughly one day in three. Sunshine changes far more through the year than rain does, from 55 hours in December to 218 in July, for 1,675 hours a year.

London through the seasons

Winter (December to February)

Winters are cool, grey and damp. January averages 9°C by day and 4°C at night, so a winter day feels raw rather than bitterly cold. Days are short: the sun sets around 15:53 in late December, and the shortest day has only 7 h 49 min of daylight. December and January each bring rain on about 11 days. Frost is common, but snow is infrequent, rarely heavy and seldom settles for long in the centre. Plan around museums, galleries and theatres, and keep outdoor sightseeing for the middle of the day.

Spring (March to May)

Spring warms gradually, from 12°C in March to 18°C in May, with cold nights early on. It is drier than its reputation: March is the driest month of the year at 37 mm, and April is close behind at 43 mm. Sunshine more than doubles between February and April, and the clocks go forward on the last Sunday of March, so evenings suddenly feel longer. Parks and squares are at their best in April and May, although blossom timing varies from year to year.

Summer (June to August)

Summers are mild and pleasant, with highs of 21–24°C and lows of 13–15°C. These are the sunniest months, with 202–218 hours of sunshine a month from May to August, and around the solstice the sun does not set until about 21:21. Summer is not dry, though: July averages 43 mm, more than March or April, and August is wetter again at 55 mm.

Autumn (September to November)

September is often settled and warm, with highs around 20°C, which makes it one of the most reliable months for walking the city. October and November turn wetter and windier, and October is the wettest month of the year at 67 mm. Highs fall from 16°C in October to 12°C in November, and once the clocks go back on the last Sunday of October, sunsets come before 17:00.

What makes London's weather distinctive

Changeable, not extreme

Atlantic weather fronts move through every few days, so a forecast of "sunny intervals and showers" is common in any season, and sunshine, showers and a cool wind can all appear in the same afternoon. Most rainy days bring only a few millimetres, usually a shower or a grey, drizzly spell rather than a day of heavy rain.

Daylight versus sunshine

At 51.5° north, day length matters as much as temperature in London. Cloud then takes a large share of that daylight.

Worked example: how sunny is a London day?

1. July averages 218 hours of bright sunshine. Divide by 31 days for the daily average.
2. Compare that with the length of a July day, about 15 h 56 min on the 21st.
3. The result: a little under half of July's daylight hours are sunny.
4. Do the same for December, with 55 hours of sunshine against 7 h 49 min of daylight, and only about a fifth of daylight hours are sunny.

So a typical summer day in London is roughly half sun, half cloud, while a typical December day has very little sun at all.

Hotter summers

The famous smogs ended after the clean-air laws of the 1950s. Today the bigger trend is heat. Hot spells are becoming more frequent, and London's highest temperature on record was set on 19 July 2022, at both Heathrow and St James's Park. Many homes, hotels, older buildings and Underground lines have no air-conditioning, so a heatwave can be harder going than the figures suggest.

Best time to visit London

There is no truly bad month to visit London, but there are clear trade-offs.

• May and September: the best balance. Highs of 18°C and 20°C, long days, relatively few rainy days and smaller crowds than high summer.
• June to August: warmest and lightest. Highs of 21–24°C, the most sunshine and evenings that stay light past 21:00 in June and July. Also the busiest and most expensive time, and the most likely to bring a heatwave.
• March and April: bright and fairly dry. Cool, at 12–15°C, but the driest months by total rain, with blossom and lengthening evenings.
• October and November: mild but wet. The wettest stretch of the year, with shortening days. Good for museums, theatre and autumn colour in the parks.
• December to February: dark and quiet. Cold, damp and short days, but festive in December, and the cheapest and least crowded time for indoor sights.

For a combined trip, compare the Paris and Amsterdam guides: Paris is warmer in summer, with July highs of 26°C, while Amsterdam is cooler and wetter in late summer and autumn. A few days before you travel, hoyoopin's Weather page shows London's live conditions and short-range forecast; for storm and heat warnings, check the Met Office.

What to pack

• All year: a compact umbrella or light waterproof layer, and comfortable shoes that cope with wet pavements
• December to February: an insulated, waterproof coat, a warm layer underneath, and gloves, scarf and hat for the evenings
• March and April: a light waterproof jacket over a jumper; mornings are often cold enough for a scarf
• May to August: light clothes by day, a thin layer for the evening, sunscreen and sunglasses, and something cool for a hot spell
• September to November: a mid-weight jacket that keeps out rain, and waterproof shoes for the wettest weeks

Because the gap between night and afternoon is small, layers work better in London than one heavy item.

Time in London

London uses the Europe/London time zone and is currently on UTC±0. It keeps Greenwich Mean Time (UTC±0) in winter and British Summer Time (UTC+1) from the last Sunday of March to the last Sunday of October. The next change forward is on 28 March 2027. The next change back is on 31 October 2027. The clocks change at 01:00 GMT, the same instant as across the European Union, so London stays exactly one hour behind Paris, Berlin and Madrid all year.

How Greenwich became the world's reference

Before the railways, every British town kept its own local solar time; Bristol, for example, ran about 10 minutes behind London. Railway companies adopted London time in the 1840s, Greenwich Mean Time became the legal time for Great Britain in 1880, and in 1884 the International Meridian Conference chose the line through the Royal Observatory at Greenwich as 0° longitude. Visitors can still stand on the meridian line in Greenwich Park. GMT and UTC show the same clock time, but UTC is the atomic-clock standard used for science and computing.

Britain has experimented more than most. During the Second World War it used British Double Summer Time, two hours ahead of GMT, in summer. From 1968 to 1971 it kept the clocks one hour ahead all year as "British Standard Time", an experiment dropped after complaints about dark winter mornings, especially in Scotland.

Scheduling with London

London's morning overlaps with the afternoon in Asia and the Gulf, and its afternoon with the morning in New York, one reason the city is a hub for currency trading. Right now London is 5 hours ahead of New York and 9 hours behind Tokyo. The United States changes its clocks two to three weeks before the UK in March and a week later in autumn, so for a few weeks a year the gap with New York is an hour smaller than usual: recheck standing transatlantic meetings in those weeks. Dubai and Mumbai never change their clocks, so their gap with London is an hour smaller in summer. August is a quiet month for business, as many people take their holidays.

Working hours taken as 09:00–18:00 on both sides, with today’s offsets (daylight saving included), from the IANA time zone database.

Calculated for this year from the city centre’s coordinates, in local clock time (daylight saving included). Hills and buildings can shift what you see by a few minutes.

Frequently asked questions

What is the warmest month in London?

July, with an average high of 24°C. Hotter spells do happen, and heatwaves have become more frequent; London's record was set in July 2022.

What is the driest month in London?

March, with 37 mm of rain on average, followed by April. The wettest month is October, at 67 mm.

Does it rain every day in London?

No. London has about 114 days a year with measurable rain, roughly one in three. Most rain is light, and many days with showers also have sunny spells.

How late does it stay light in London in summer?

Around the June solstice the sun sets at about 21:21. In late December it sets around 15:53.

Is London on GMT or UTC?

London keeps GMT (UTC±0) in winter and British Summer Time (UTC+1) in summer. GMT and UTC show the same clock time; UTC is the scientific standard every time zone is defined from.

Does London get snow?

Occasionally. Light snow falls in most winters, but it is rarely heavy and seldom settles for long in the city centre.

Sources

1. Climate of London (temperature record, snowfall) — Wikipedia