This report describes the typical weather at the Boeing Field/King County International Airport (Seattle, Washington, United States) 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.
Seattle, Washington has a mediterranean climate with dry warm summers and mild winters. The area within 25 mi of this station is covered by forests (61%), built-up areas (17%), oceans and seas (17%), and croplands (3%).
The month of August is characterized by gradually falling daily high temperatures, with daily highs decreasing from 78°F to 74°F over the course of the month, exceeding 87°F or dropping below 66°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 1:33 hours, implying an average day-over-day decrease of 3.0 minutes.
The shortest day of the month is August 31 with 13:23 hours of daylight; the longest day is August 1 with 14:56 hours of daylight.
The earliest sunrise is at 5:47am on August 1; the latest sunset is at 8:43pm on August 1; the latest sunrise is at 6:27am 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 ranges from 58% (partly cloudy) to 64% (partly cloudy).
On August 16, a representative day, the sky is clear or mostly clear 40% of the time, partly cloudy 13% of the time, and mostly cloudy or overcast 45% of the time.
The probability that precipitation will be observed at this location varies throughout the month. Precipitation is most likely around August 31, occurring in 29% of days. Precipitation is least likely around August 4, occurring in 23% of days.
Throughout August, the most common forms of precipitation are light rain, moderate rain, and thunderstorms.
Light rain is the most severe precipitation observed during 66% of those days with precipitation. It is most likely around August 31, when it is observed during 20% of all days.
Moderate rain is the most severe precipitation observed during 12% of those days with precipitation. It is most likely around August 31, when it is observed during 4% of all days.
Thunderstorms are the most severe precipitation observed during 11% of those days with precipitation. They are most likely around August 12, when it is observed during 3% 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 42% (comfortable) to 90% (very humid) over the course of a typical August, rarely dropping below 30% (comfortable) and reaching as high as 100% (very humid).
The air is driest around August 3, at which time the relative humidity drops below 49% (comfortable) three days out of four; it is most humid around August 31, rising above 84% (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 49°F (dry) to 56°F (comfortable) and is rarely below 43°F (dry) or above 60°F (comfortable).
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 0 mph to 11 mph (calm to gentle breeze), rarely exceeding 16 mph (moderate breeze).
The highest average wind speed of 6 mph (light breeze) occurs around August 1, at which time the average daily maximum wind speed is 11 mph (gentle breeze).
The lowest average wind speed of 6 mph (light breeze) occurs around August 28, at which time the average daily maximum wind speed is 11 mph (gentle breeze).