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 October. 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 October is characterized by rapidly falling daily high temperatures, with daily highs decreasing from 66°F to 56°F over the course of the month, exceeding 74°F or dropping below 50°F only one day in ten.
Over the course of October, the length of the day is rapidly decreasing. From the start to the end of the month, the length of the day decreases by 1:39 hours, implying an average day-over-day decrease of 3.2 minutes.
The shortest day of the month is October 31 with 9:60 hours of daylight; the longest day is October 1 with 11:39 hours of daylight.
The earliest sunrise is at 7:09am on October 1; the latest sunset is at 6:47pm on October 1; the latest sunrise is at 7:53am on October 31; the earliest sunset is at 5:52pm on October 31.
Daylight savings time is observed in 2012 but it neither starts nor ends in October, so the entire month is in daylight time.
The median cloud cover ranges from 79% (partly cloudy) to 96% (overcast). The trend is for the sky to be becoming rapidly cloudier with the median cloud cover increasing by 16% from the start to the end of the month.
On October 1, the clearest day of the month, the sky is clear, mostly clear, or partly cloudy 40% of the time, and overcast or mostly cloudy 60% of the time.
On October 31, the cloudiest day of the month, the sky is overcast, mostly cloudy, or partly cloudy 82% of the time, and clear or mostly clear 18% of the time.
The probability that precipitation will be observed at this location varies throughout the month. Precipitation is most likely around October 31, occurring in 57% of days. Precipitation is least likely around October 1, occurring in 41% of days.
Throughout October, the most common forms of precipitation are light rain and moderate rain.
Light rain is the most severe precipitation observed during 70% of those days with precipitation. It is most likely around October 31, when it is observed during 38% of all days.
Moderate rain is the most severe precipitation observed during 18% of those days with precipitation. It is most likely around October 30, when it is observed during 11% of all days.
Either snow is exceptionally unlikely to fall at this location in October or this station does not reliably report precipitation types.
The relative humidity typically ranges from 53% (mildly humid) to 95% (very humid) over the course of a typical October, rarely dropping below 37% (comfortable) and reaching as high as 100% (very humid).
The air is driest around October 1, at which time the relative humidity drops below 62% (mildly humid) three days out of four; it is most humid around October 14, rising above 91% (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 October, the dew point typically varies from 39°F (dry) to 52°F (very comfortable) and is rarely below 31°F (dry) or above 57°F (comfortable).
Over the course of October typical wind speeds vary from 0 mph to 12 mph (calm to gentle breeze), rarely exceeding 18 mph (fresh breeze).
The highest average wind speed of 6 mph (light breeze) occurs around October 31, at which time the average daily maximum wind speed is 12 mph (gentle breeze).
The lowest average wind speed of 6 mph (light breeze) occurs around October 1, at which time the average daily maximum wind speed is 11 mph (gentle breeze).