Oregon's climate is usually moderate, although there are variations across the state. The Cascade mountains keep moist air from the Pacific in the western third, resulting in heavy precipitation and moderate temperatures. The eastern two-thirds of the state are drier and have more extreme temperatures.
The average annual rainfall in Portland is 37 inches, while the driest part of the state receives less than 8 inches. The most rainfall in Oregon is up to 200 inches in western areas of the Coast Range. The average January temperature is 45 degrees Fahrenheit, while the average July temperature is only 65 degrees in the western part of the state. The eastern part of the state experiences more extreme temperature variations.