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Average Weather at London Heathrow Airport United Kingdom

In London Heathrow Airport, the temperature typically varies from 36°F to 74°F over the course of the year, and is rarely below 28°F or above 84°F.

The warm season lasts for 89 days, from June 13 to September 10, with an average daily high temperature above 68°F. The hottest day of the year is July 28, with an average high of 74°F and low of 58°F.

The cool season lasts for 121 days, from November 16 to March 17, 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 daily average high (red line) and low (blue line) temperature with percentile bands, with 25th to 75th and 10th to 90th percentile bands. The thin dotted lines are the corresponding average perceived temperatures.

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

12 AM4 AM8 AM12 PM4 PM8 PM12 AMJanFebMarAprMayJunJulAugSepOctNovDecchillychillycoldcoldcoolcoolcomfortablecomfortable
The average hourly temperature, color coded into bands: frigid < 15°F < freezing < 32°F < chilly < 45°F < cold < 55°F < cool < 65°F < comfortable < 75°F < warm < 85°F < hot < 95°F < sweltering. The shaded overlays indicate night and civil twilight.

Sun

The length of the day at London Heathrow Airport varies extremely over the course of the year. In 2017, the shortest day is December 21, with 7 hours, 50 minutes of daylight; the longest day is June 21, with 16 hours, 38 minutes of daylight.

Hours of Daylight and Twilight

The number of hours during which the Sun is visible (black line). From bottom (most yellow) to top (most gray), the color bands indicate: full daylight, twilight (civil, nautical, and astronomical), and full night.

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 26.

Daylight saving time (DST) is observed at London Heathrow Airport during 2017, starting in the spring on March 26, lasting 216 days, and ending in the fall on October 29.

Sunrise & Sunset with Twilight and Daylight Saving Time

The solar day over the course of the year 2017. From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray. The transitions to and from daylight saving time are indicated by the 'DST' labels.

Clouds

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 200 days, ending around October 19. On July 15, 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 19 and lasts for 165 days, ending around April 2. On December 27, 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

clearerclearercloudiercloudiercloudiercloudier0%10%20%30%40%50%60%70%80%90%100%JanFebMarAprMayJunJulAugSepOctNovDecDec 2774%Dec 2774%Jul 1542%Jul 1542%Apr 258%Apr 258%Oct 1958%Oct 1958%overcastovercastmostly cloudymostly cloudypartly cloudypartly cloudymostly clearmostly clearclearclear
The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds: clear < 20% < mostly clear < 40% < partly cloudy < 60% < mostly cloudy < 80% < overcast.

Precipitation

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 254 days, from May 27 to February 5, with a greater than 27% chance of a given day being a wet day. The chance of a wet day peaks at 33% on December 30.

The drier season lasts 111 days, from February 5 to May 27. The smallest chance of a wet day is 20% on April 26.

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 30.

Daily Chance of Precipitation

wetwetwetwetdrydry0%10%20%30%40%50%60%70%80%90%100%JanFebMarAprMayJunJulAugSepOctNovDecDec 3033%Dec 3033%Apr 2620%Apr 2620%May 2727%May 2727%Feb 527%Feb 527%mixedmixedrainrainsnowsnow
The percentage of days in which various types of precipitation are observed, excluding trace quantities: rain alone, snow alone, and mixed (both rain and snow fell in the same day).

Rainfall

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 in 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 21, with an average total accumulation of 2.2 inches.

The least rain falls around March 12, with and average total accumulation of 1.3 inches.

Average Monthly Rainfall

The average rainfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average liquid-equivalent snowfall.

Humidity

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

0%10%20%30%40%50%60%70%80%90%100%JanFebMarAprMayJunJulAugSepOctNovDecNov 160%Nov 160%Aug 111%Aug 111%comfortablecomfortabledrydry
The percentage of time spent at various humidity comfort levels, categorized by dew point: dry < 55°F < comfortable < 60°F < humid < 65°F < muggy < 70°F < oppressive < 75°F < miserable.

Wind

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 mildly seasonal variation over the course of the year.

The windier part of the year lasts for 172 days, from October 12 to April 2, with average wind speeds of more than 6.2 miles per hour. The windiest day of the year is January 3, with an average hourly wind speed of 7.2 miles per hour.

The calmer time of year lasts for 193 days, from April 2 to October 12. The calmest day of the year is August 3, with an average hourly wind speed of 5.2 miles per hour.

Average Wind Speed

windywindywindywindy0 mph1 mph2 mph3 mph4 mph5 mph6 mph7 mph8 mph9 mph10 mph11 mph12 mphJanFebMarAprMayJunJulAugSepOctNovDecJan 37.2 mphJan 37.2 mphAug 35.2 mphAug 35.2 mphOct 126.2 mphOct 126.2 mphApr 26.2 mphApr 26.2 mph
The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.

The predominant average hourly wind direction at London Heathrow Airport varies throughout the year.

The wind is most often from the north for 27 days, from April 15 to May 12, with a peak percentage of 29% on April 19. The wind is most often from the west for 338 days, from May 12 to April 15, with a peak percentage of 43% on July 3.

Wind Direction

WWNNWW0%20%40%60%80%100%JanFebMarAprMayJunJulAugSepOctNovDecwestwestsouthsoutheasteastnorthnorth
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions (north, east, south, and west), excluding hours in which the mean wind speed is less than 1 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

Water Temperature

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 101 days, from July 9 to October 18, with an average temperature above 60°F. The day of the year with the warmest water is August 26, with an average temperature of 63°F.

The time of year with cooler water lasts for 114 days, from January 2 to April 26, with an average temperature below 49°F. The day of the year with the coolest water is March 3, with an average temperature of 46°F.

Average Water Temperature

The daily average water temperature (purple line) with percentile bands, with 25th to 75th and 10th to 90th percentile bands.

Solar Energy

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 very significant seasonal variation over the course of the year.

The brighter period of the year lasts for 108 days, from May 2 to August 18, with an average daily incident shortwave energy per square meter above 5.3 kWh. The brightest day of the year is June 28, with an average of 6.4 kWh.

The darker period of the year lasts for 117 days, from October 26 to February 20, with an average daily incident shortwave energy per square meter below 1.8 kWh. The darkest day of the year is December 26, with an average of 0.6 kWh.

Average Daily Incident Shortwave Solar Energy

The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.

Topography

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 (map ).

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 very significant 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%).

Data Sources

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.

Other Data

All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Tables of the Sun, Moon and Planets , 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 .