This report describes the typical weather at the London Heathrow Airport (London, United Kingdom) weather station over the course of an average August. It is based on the historical records from 1974 to 2012. Earlier records are either unavailable or unreliable.
London has a mild humid temperate climate with warm summers and no dry season. The area within 25 mi of this station is covered by croplands (60%), built-up areas (35%), and grasslands (4%).
The month of August is characterized by gradually falling daily high temperatures, with daily highs ranging from 74°F to 70°F over the course of the month, exceeding 83°F or dropping below 64°F only one day in ten.
Over the course of August, the length of the day is rapidly decreasing. From the start to the end of the month, the length of the day decreases by 1:47 hours, implying an average day-over-day decrease of 3.5 minutes.
The shortest day of the month is August 31 with 13:37 hours of daylight; the longest day is August 1 with 15:24 hours of daylight.
The earliest sunrise is at 5:26am on August 1; the latest sunset is at 8:49pm on August 1; the latest sunrise is at 6:13am on August 31; the earliest sunset is at 7:50pm on August 31.
Daylight savings time is observed in 2012 but it neither starts nor ends in August, so the entire month is in daylight time.
The median cloud cover is 71% (partly cloudy) and does not vary substantially over the course of the month.
On August 16, a representative day, the sky is clear or mostly clear 30% of the time, partly cloudy 23% of the time, and mostly cloudy or overcast 42% of the time.
The average probability that some form of precipitation will be observed in a given day is 56%, with little variation over the course of the month.
Throughout August, the most common forms of precipitation are moderate rain and thunderstorms.
Moderate rain is the most severe precipitation observed during 72% of those days with precipitation. It is most likely around August 7, when it is observed during 41% of all days.
Thunderstorms are the most severe precipitation observed during 11% of those days with precipitation. They are most likely around August 1, when it is observed during 7% of all days.
Either snow is exceptionally unlikely to fall at this location in August or this station does not reliably report precipitation types.
The relative humidity typically ranges from 48% (comfortable) to 92% (very humid) over the course of a typical August, rarely dropping below 34% (comfortable) and reaching as high as 100% (very humid).
The air is driest around August 1, at which time the relative humidity drops below 56% (mildly humid) three days out of four; it is most humid around August 27, rising above 89% (very humid) three days out of four.
Dew point is often a better measure of how comfortable a person will find the weather than relative humidity because it more directly relates to whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid.
Over the course of a typical August, the dew point typically varies from 48°F (dry) to 59°F (comfortable) and is rarely below 41°F (dry) or above 63°F (mildy humid).
The time of the month between August 1 and August 31 is the most comfortable, with dew points that are neither too dry nor too muggy.
Over the course of August typical wind speeds vary from 2 mph to 13 mph (light air to moderate breeze), rarely exceeding 19 mph (fresh breeze).
The highest average wind speed of 8 mph (gentle breeze) occurs around August 1, at which time the average daily maximum wind speed is 13 mph (moderate breeze).
The lowest average wind speed of 8 mph (gentle breeze) occurs around August 9, at which time the average daily maximum wind speed is 13 mph (moderate breeze).