Seattle's climate is a "modified Mediterranean" type (Köppen: Csb), featuring cool, wet winters and warm, dry summers, with the Pacific Ocean and Puget Sound keeping seasonal temperature swings remarkably small. Although the city generally avoids weather extremes, it set a new all-time high of 108°F (42°C) on June 28, 2021, breaking a record set just two years earlier in July 2009, while the coldest reading was 0°F (-18°C) in January 1950. This pattern is driven by the North Pacific High in summer, which blocks storms, and the Aleutian Low in winter, which steers extratropical cyclones toward the coast, delivering most of the annual rainfall between October and March. The 21st century has brought a trend toward more extreme heat and heavy rain, including a record single-day downpour in October 2003, yet thunderstorms remain rare (about seven days a year) and heavy snow is uncommon, though light snow falls most years. Official records date back to 1894 in downtown Seattle—which tends to be warmer and drier—before moving to the airport in 1945, explaining some historical temperature variations.