Average Weather at London Heathrow Airport United Kingdom
At London Heathrow Airport, the summers are short, comfortable, and partly cloudy and the winters are long, very cold, windy, and mostly cloudy. Over the course of the year, the temperature typically varies from 36°F to 74°F and is rarely below 28°F or above 84°F.
Based on the tourism score, the best time of year to visit London Heathrow Airport for warm-weather activities is from late June to early September.
The warm season lasts for 2.9 months, from June 13 to September 8, with an average daily high temperature above 68°F. The hottest day of the year is July 27, with an average high of 74°F and low of 58°F.
The cool season lasts for 4.0 months, from November 15 to March 15, with an average daily high temperature below 52°F. The coldest day of the year is February 7, with an average low of 36°F and high of 46°F.
Average High and Low Temperature
The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.
Average Hourly Temperature
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
At London Heathrow Airport, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.
The clearer part of the year at London Heathrow Airport begins around April 2 and lasts for 6.5 months, ending around October 18. On July 14, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 58% of the time, and overcast or mostly cloudy 42% of the time.
The cloudier part of the year begins around October 18 and lasts for 5.5 months, ending around April 2. On December 26, the cloudiest day of the year, the sky is overcast or mostly cloudy 74% of the time, and clear, mostly clear, or partly cloudy 26% of the time.
Cloud Cover Categories
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days at London Heathrow Airport varies throughout the year.
The wetter season lasts 8.3 months, from May 26 to February 5, with a greater than 26% chance of a given day being a wet day. The chance of a wet day peaks at 33% on December 29.
The drier season lasts 3.6 months, from February 5 to May 26. The smallest chance of a wet day is 20% on April 25.
Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 32% on December 29.
Daily Chance of Precipitation
To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. London Heathrow Airport experiences some seasonal variation in monthly rainfall.
Rain falls throughout the year at London Heathrow Airport. The most rain falls during the 31 days centered around October 20, with an average total accumulation of 2.2 inches.
The least rain falls around March 11, with an average total accumulation of 1.3 inches.
Average Monthly Rainfall
The length of the day at London Heathrow Airport varies extremely over the course of the year. In 2020, the shortest day is December 21, with 7 hours, 50 minutes of daylight; the longest day is June 20, with 16 hours, 38 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 4:44 AM on June 16, and the latest sunrise is 3 hours, 23 minutes later at 8:07 AM on December 30. The earliest sunset is at 3:52 PM on December 12, and the latest sunset is 5 hours, 30 minutes later at 9:23 PM on June 24.
Daylight saving time (DST) is observed at London Heathrow Airport during 2020, starting in the spring on March 29, lasting 6.9 months, and ending in the fall on October 25.
Sunrise & Sunset with Twilight and Daylight Saving Time
We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.
The perceived humidity level at London Heathrow Airport, as measured by the percentage of time in which the humidity comfort level is muggy, oppressive, or miserable, does not vary significantly over the course of the year, remaining a virtually constant 0% throughout.
Humidity Comfort Levels
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.
The average hourly wind speed at London Heathrow Airport experiences significant seasonal variation over the course of the year.
The windier part of the year lasts for 5.6 months, from October 12 to March 31, with average wind speeds of more than 11.5 miles per hour. The windiest day of the year is January 3, with an average hourly wind speed of 13.3 miles per hour.
The calmer time of year lasts for 6.4 months, from March 31 to October 12. The calmest day of the year is August 2, with an average hourly wind speed of 9.7 miles per hour.
Average Wind Speed
The predominant average hourly wind direction at London Heathrow Airport varies throughout the year.
The wind is most often from the north for 3.9 weeks, from April 14 to May 11, with a peak percentage of 29% on April 18. The wind is most often from the west for 11 months, from May 11 to April 14, with a peak percentage of 40% on January 1.
London Heathrow Airport is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.
The average water temperature experiences some seasonal variation over the course of the year.
The time of year with warmer water lasts for 3.3 months, from July 8 to October 17, with an average temperature above 60°F. The day of the year with the warmest water is August 25, with an average temperature of 63°F.
The time of year with cooler water lasts for 3.7 months, from January 2 to April 25, with an average temperature below 49°F. The day of the year with the coolest water is March 2, with an average temperature of 46°F.
Average Water Temperature
Best Time of Year to Visit
To characterize how pleasant the weather is at London Heathrow Airport throughout the year, we compute two travel scores.
The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit London Heathrow Airport for general outdoor tourist activities is from late June to early September, with a peak score in the last week of July.
The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit London Heathrow Airport for hot-weather activities is from mid July to mid August, with a peak score in the last week of July.
For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.
Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.
Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.
Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.
Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.
Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).
The growing season at London Heathrow Airport typically lasts for 8.1 months (249 days), from around March 22 to around November 26, rarely starting before February 14 or after April 20, and rarely ending before November 1 or after December 21.
Time Spent in Various Temperature Bands and the Growing Season
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.
Based on growing degree days alone, the first spring blooms at London Heathrow Airport should appear around April 18, only rarely appearing before April 1 or after May 5.
Growing Degree Days
This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.
The average daily incident shortwave solar energy experiences extreme seasonal variation over the course of the year.
The brighter period of the year lasts for 3.5 months, from May 1 to August 17, with an average daily incident shortwave energy per square meter above 5.3 kWh. The brightest day of the year is June 27, with an average of 6.4 kWh.
The darker period of the year lasts for 3.8 months, from October 25 to February 19, with an average daily incident shortwave energy per square meter below 1.8 kWh. The darkest day of the year is December 25, with an average of 0.6 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of London Heathrow Airport are 51.471 deg latitude, -0.456 deg longitude, and 75 ft elevation.
The topography within 2 miles of London Heathrow Airport contains only modest variations in elevation, with a maximum elevation change of 125 feet and an average elevation above sea level of 78 feet. Within 10 miles also contains only modest variations in elevation (407 feet). Within 50 miles contains only modest variations in elevation (1,027 feet).
The area within 2 miles of London Heathrow Airport is covered by artificial surfaces (75%) and grassland (14%), within 10 miles by artificial surfaces (68%) and grassland (16%), and within 50 miles by cropland (41%) and grassland (26%).
This report illustrates the typical weather at London Heathrow Airport, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.
Temperature and Dew Point
London Heathrow Airport has a weather station that reported reliably enough during the analysis period that we have included it in our network. When available, historical temperature and dew point measurements are taken directly from this weather station. These records are obtained from NOAA's Integrated Surface Hourly data set, falling back on ICAO METAR records as required.
In the case of missing or erroneous measurements from this station, we fall back on records from nearby stations, adjusted according to typical seasonal and diurnal intra-station differences. For a given day of the year and hour of the day, the fallback station is selected to minimize the prediction error over the years for which there are measurements for both stations.
The stations on which we may fall back include but are not limited to RAF Northolt, Bracknell / Beaufort Park, London Weather Centre, Farnborough Airport, Luton Airport, London Gatwick Airport, London City Airport, and RAF Odiham.
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Algorithms 2nd Edition , by Jean Meeus.
All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.
Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.
Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.
Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .
Time zones for aiports and weather stations are provided by AskGeo.com .
Maps are © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.
The information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site.
We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands.
We further caution that our travel scores are only as good as the data that underpin them, that weather conditions at any given location and time are unpredictable and variable, and that the definition of the scores reflects a particular set of preferences that may not agree with those of any particular reader.