Article: From 1981 to 2010, the average annual precipitation measured at Seattle–Tacoma International Airport was 37.49 inches (952 mm). Annual precipitation has ranged from 23.78 in (604 mm) in 1952 to 55.14 in (1,401 mm) in 1950; for water year (October 1 – September 30) precipitation, the range is 23.16 in (588 mm) in 1976–77 to 51.82 in (1,316 mm) in 1996–97. Due to local variations in microclimate, Seattle also receives significantly lower precipitation than some other locations west of the Cascades. Around 80 mi (129 km) 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 142 in (3.61 m). Sixty miles to the south of Seattle, the state capital Olympia, which is out of the Olympic Mountains' rain shadow, receives an annual average precipitation of 50 in (1,270 mm). The city of Bremerton, about 15 mi (24 km) west of downtown Seattle, receives 56.4 in (1,430 mm) of precipitation annually.

Question: What weather factor produces a great variance in local climates in the Seattle area?
variations in microclimate