A view of Eugene from atop Skinner Butte. Lane County is located in the wet climate zone of Oregon as opposed to the much drier portion of the state east of the Cascade Mountains. The distribution of precipitation is uneven throughout Lane County due to drastic changes in physical geography, mainly concerning changes in elevation. Likewise, the distribution of precipitation is largely dependent on seasonal changes in the weather. Elevation varies greatly throughout the various regions of Lane County.
Coastal areas begin at sea level and rise quickly as one travels east into the Coastal Range.
The Valley floors average 400 feet above sea level, and the Cascade Mountains farther to the east tower above at elevations exceeding 10,000 feet above sea level. The differences in levels of precipitation mirror these changes in elevation. The western slopes of the Coastal and Cascade ranges receive far more precipitation than the valley floors due to the condensation of moisture associated with the marine environment of the Pacific Ocean. Air containing moisture must rise to pass over mountain ranges and the vast majority of the precipitation falls on the western side of the mountains, leaving the eastern side much drier. The Coastal and Cascade Ranges receive more than 100 inches of precipitation annually, much of which is in the form of snow during the winter months.