Seattle’s temperatures are greatly moderated by Puget Sound, the nearby Pacific Ocean and the Cascade mountain range, all of which generally protect the city from the scorching heatwaves and bitter cold that often wreak havoc in other parts of the country. The average daily high temperature in Seattle ranges from a peak of 77 degrees from July 19-Aug. 16 to a minimum of 45 degrees from Dec. 14-30. In similarly mild fashion, the normal low temperature in Seattle runs from 35 degrees from Dec. 11-25 to 57 degrees from July 27-Aug. 6.
However, Seattle is not entirely immune to extreme temperatures on both sides of the spectrum. This was demonstrated all too clearly in the summer of 2009, when the mercury soared to a record-breaking 103 degrees on July 29—the hottest temperature ever recorded in Seattle. Likewise, on Jan. 31, 1950, in the midst of a bone-chilling arctic blast, the temperature plunged to 0 degrees at Sea-Tac Airport—the city’s coldest temperature on record.
The graphs below show the top 10 hottest and coldest days observed in Seattle since records were first taken at Sea-Tac Airport. Importantly, Seattle also reached 100 degrees on July 16, 1941, when weather measurements were recorded at the Federal Building downtown.
Note: Data in both charts from records taken at Sea-Tac Airport.