Temperature extremes are moderated by the adjacent Puget Sound, greater Pacific Ocean, and Lake Washington. The region is largely shielded from Pacific storms by the Olympic Mountains and from Arctic air by the Cascade Range. Despite being on the margin of the rain shadow of the Olympic Mountains, the city has a reputation for frequent rain. This reputation stems from the frequency of light precipitation in the fall, winter, and spring. In an average year, at least 0.01 inches (0.25 mm) of precipitation falls on 150 days, more than nearly all U.S. cities east of the Rocky Mountains. It is cloudy 201 days out of the year and partly cloudy 93 days. Official weather and climatic data is collected at Seattle–Tacoma International Airport, located about 19 km (12 mi) south of downtown in the city of SeaTac, which is at a higher elevation, and records more cloudy days and fewer partly cloudy days per year.

What does the local water ways regulate in the Seattle area?