Compared with western Washington, the “dry side of the mountains” has hotter summers, colder winters, more snow, and less rain. The area from the Cascade Range east across the Columbia Basin to the Palouse hills has hot, dry weather with an average of only 7–15 inches of annual rainfall. Summer daytime temperatures are in the 90s, with many days each year over 100°F; the state’s record high of 118°F occurred at Ice Harbor Dam (near Pasco) in 1961. July and August are the driest months, often devoid of any precipitation at all; what rain they do receive generally comes packaged in thunderstorms. Winters bring 10–35 inches of snowfall and daytime temperatures in the 20s and 30s.
The Okanogan and Methow Valleys, in the north-central part of the state, are a cross-country skier’s paradise. Annual winter snowfalls range 30–70 inches, beginning in November and staying on the ground through March or April. January maximum temperatures hover around 30°, with some nighttime below-zero temperatures recorded each year. In summer, the Okanogan Valley is another eastern Washington hot spot, with temperatures averaging 85–90°F including several 100°F days each season, plus occasional thunderstorms and hailstorms.
Much of this part of Washington, from the Columbia River east to the Spokane area and the Palouse hills south of Spokane, is technically a desert because the rainfall is less than 12 inches a year; in a few places no more than eight inches can be measured. In fact, this is the northern end of the Great American Desert, which runs from the Mexican border north almost to the Canadian border. Today it doesn’t look like the Sahara or Death Valley because of the vast irrigation systems that have been built there, turning the desert into a crosshatched garden.
The largest irrigation project is the massive Columbia Basin Project, created by Grand Coulee Dam, which puts water on a half million acres of farms and vineyards. The mighty Columbia—the second-biggest river in America—drains an area of 259,000 square miles within parts of seven states and Canada. With the dams backing water over the river’s rapids, barges can now travel all the way to Clarkston and Lewiston along the Washington/Idaho border.
As you travel toward the state’s eastern boundary with Idaho, the elevation gradually rises and the more extreme desert weather returns to a cool dampness. The farms in the Palouse Country near Pullman are among the most productive wheat farms in the world, and because the climate is usually so predictable, eastern Washington wheat farmers have never had a complete crop failure in history.
Summer temperatures in central and eastern Washington are in the upper 80s and winter averages in the 30s, with a few extremes of plus 100°F and minus 20°F recorded every year. The Blue Mountains in the southeast corner get up to 40 inches of precipitation, while Pend Oreille County in the northeast corner receives 28 inches of rain and 40–80 inches of snow.
© Ericka Chickowski from Moon Washington, 8th edition