Climate of Seattle
The climate of Seattle is temperate, classified in the warm-summer subtype of the Mediterranean zone by the most common climate classification although some sources put the city in the oceanic zone. It has cool, wet winters and warm, dry summers, covering characteristics of both. The climate is sometimes characterized as a "modified Mediterranean" climate because it is cooler and wetter than a "true" Mediterranean climate, but shares the characteristic dry summer and the associated reliance upon cooler-season precipitation. The city is part of USDA hardiness zone 9a, with surrounding pockets falling under 8b.
Records for the Seattle City area date back to 1894, with records at Seattle-Tacoma International Airport beginning in 1945, a location notably not within Seattle. Prior to 1945 the official temperatures were observed in locations in downtown Seattle, which tends in general to be somewhat warmer and drier than the airport location. The hottest officially recorded temperature was on June 28, 2021; the coldest recorded temperature was on January 31, 1950; the record cold daily maximum is on January 14, 1950, while, conversely, the record warm daily minimum is on June 27, 2021.
Seattle generally does not experience many extremes of weather. However, the 21st century has seen a trend towards more extreme high-temperature and large-precipitation events. In July 2009 Seattle's all-time high temperature was broken by a margin of 4 degrees Fahrenheit, then broken again by a margin of 5 F in June 2021. The single-day precipitation record set in October 2003 saw higher precipitation by nearly 2 inches than any other day on record. However, thunderstorms are still rare, as the city reports thunder on just seven days per year. Similarly, the city typically receives at least light snowfall every year, though heavy snowfall is uncommon.
Temperature
The city's regime of temperature features small seasonal swings, due to its proximity to the ocean. The Pacific Ocean, Puget Sound and Lake Washington serve as moderators of the temperature meaning the city is milder than areas inland during the winter and cooler during the summer. Extreme heatwaves are rare, as are cold temperatures.Hot temperature extremes are enhanced by dry, compressed wind from the west slopes of the Cascades, while cold temperatures are generated mainly from the Fraser Valley in British Columbia. Records are taken from the Seattle City area from 1894 to 1944 and at Sea-Tac Airport from 1945.
Averages
In an average year, the temperature will usually be between and with temperatures greatly exceeding these values being uncommon. Temperatures above and below are very rare, with the last occurrences being June 28, 2021 and November 24, 2010, respectively.Highest daily temperatures
| Period | Record temperature | Date |
| Jan 28, 1931 | ||
| Feb 27, 1968 | ||
| Mar 20, 2019 Mar 19, 2019 | ||
| Apr 18, 2016 | ||
| May 21, 1963 | ||
| Jun 28, 2021 | ||
| Jul 29, 2009 | ||
| Aug 9, 1981 Aug 9, 1960 | ||
| Sep 2, 1988 | ||
| Oct 1, 1987 | ||
| Nov 3, 2010 Nov 4, 1949 | ||
| Dec 10, 2014 |
Lowest daily temperatures
Daily record warm minima
| Period | Record temperature | Date |
| Jan 24, 1935 | ||
| Feb 28, 1901 | ||
| Mar 19, 2019 | ||
| Apr 28, 1976 | ||
| May 15, 2023 May 9, 1940 | ||
| Jun 27, 2021 | ||
| Jul 29, 2009 | ||
| Aug 14, 2023 | ||
| Sep 2, 1974 | ||
| Oct 18, 1940 | ||
| Nov 4, 2020 | ||
| Dec 26, 1980 Dec 28, 1917 |
Daily record cold maxima
| Period | Record temperature | Date |
| Jan 14, 1950 | ||
| Feb 2, 1989 | ||
| Mar 4, 1955 | ||
| Apr 3, 1920 Apr 11, 1911 | ||
| May 15, 1894 | ||
| Jun 1, 1908 | ||
| Jul 2, 1966 | ||
| Aug 2, 1956 | ||
| Sep 26, 1948 | ||
| Oct 30, 1935 | ||
| Nov 12, 1955 | ||
| Dec 29, 1968 |
Highest averages
| Period | Record mean | Year |
| Year | 1940, 2015 | |
| Spring | 1934 | |
| Summer | 2015 | |
| Autumn | 1967 | |
| Winter | 1940–1941 | |
| January | 2010 | |
| February | 2015 | |
| March | 1941 | |
| April | 2016 | |
| May | 2018 | |
| June | 2015 | |
| July | 2015 | |
| August | 1967 | |
| September | 1967 | |
| October | 2014 | |
| November | 1899 | |
| December | 1939 |
Lowest averages
NOTE: in the tables below, all numbers before 1945 come from locations in downtown Seattle, which tends to be somewhat warmer than the current official location of Sea-Tac airport. To distinguish these older numbers we mark them below in ''italics.''Precipitation
The city sees frequent, though light rainfall between October and May, with rainfall becoming lighter and sparser between June and September. With many more "rain days" than other major American cities, Seattle has a well-earned reputation for frequent rain. In an average year, at least of precipitation falls on 150 days, more than nearly all U.S. cities east of the Rocky Mountains. In November, Seattle averages more rainfall than any other U.S. city of more than 250,000 people; it also ranks highly in winter precipitation. Conversely, the city receives some of the lowest precipitation amounts of any large city from June to September. Seattle is one of the five rainiest major U.S. cities as measured by the number of days with precipitation. However, because Seattle often has merely a light drizzle falling from the sky for many days, it actually receives significantly less rainfall overall than many other U.S. cities like New York City, Miami, or Houston. Seattle experiences its heaviest rainfall during November, December, and January, receiving roughly half of its annual rainfall during this period. In late fall and early winter, atmospheric rivers, strong frontal systems, and Pacific low-pressure systems are common. Light rain and drizzle are the predominant forms of precipitation during the remainder of the year. On average, less than of rain falls in July and August combined when rain is less common.Annually, total precipitation averages, with winter being the wettest season and July the driest month. At Sea-Tac, rain has fallen in every month since records began there in January 1945, previously in the Seattle City area, the July's of 1896 and 1922 reported no precipitation. Long stretches of little precipitation can occur. No measurable precipitation, greater than, fell between June 18 and August 13, 2017. The city also sees snow, primarily in winter, but sometimes in the late autumn and early spring. Snowfall averages per year but is highly variable between winter seasons. The most rainfall in 24 hours was on October 20, 2003, and the most snowfall was on February 2, 1916. Seattle typically receives some snowfall on an annual basis but heavy snow is rare. Average annual snowfall, as measured at Sea-Tac Airport, is. From winter season to winter season, amounts can be extremely variable.
Due to local variations in microclimate, Seattle also receives significantly lower precipitation than some other locations west of the Cascades. Around to the west, the Hoh Rain Forest in Olympic National Park on the western flank of the Olympic Mountains receives an annual average precipitation of. to the south of Seattle, the state capital Olympia, which is out of the Olympic Mountains' rain shadow, receives an annual average precipitation of. The city of Bremerton, about west of downtown Seattle on the other side of the Puget Sound, receives of precipitation annually.
One of many exceptions to Seattle's reputation as a damp location occurs in El Niño years, when marine weather systems track as far south as California and less than the usual precipitation falls in the Puget Sound area. However, the El Nino of 2015-2016 caused an increase in rainfall. Since the region's water comes from mountain snow packs during the dry summer months, El Niño winters can not only produce substandard skiing but can result in water rationing and a shortage of hydroelectric power the following summer.