Olympic Mountains Rain Shadow

August 21, 2011


: Rebecca Roush
Summary Authors: Rebecca Roush; Jim Foster

Looking west toward the Olympic Mountains in the U.S. state of Washington, these approaching cirrus clouds, observed from the city of Sequim, don’t necessarily herald the arrival of rain. Sequim is in a rain shadow. It’s home to many retirees who want to live in western Washington but also want to avoid the rainy weather that frequents this region. Rain shadows are found on the lee side of many mountain ranges. In the Olympic Mountains, for instance, moist air moving upslope (from the Pacific Ocean) cools and condenses, resulting in precipitation on the windward slopes. As this now saturated air crosses the higher summits and moves downslope (toward Sequim), it compresses, warms and dries.

The annual rainfall for Sequim is but 16 in (406 mm), which compares to Seattle’s 36.2 in (920 mm), just 60 mi (97 km) to the east. However, The Hoh Rainforest, 105 mi (169 km) west of Sequim, has an annual rainfall of more than 150 in (3,810 mm). On June 21, 1995, the Sequim City Council passed Ordinance 95-009, prohibiting "weather that may disrupt the plans of its residents and visitors." See, we really can do something about the weather.