Although Washington state is generally thought of as a wet place, the Columbia Valley is extremely dry because it lies in the rain shadow of the Cascade Mountains. Rainfall averages about 7 to 8 inches a year, so vineyards depend on irrigation. Purists who think grapes should be farmed without irrigation might choke on their chardonnay when they hear Washington vintners crow about how they can affect wine styles depending on how much water the vines are given and when it is applied. But there's no disputing that many of the wines are outstanding. Another important climatic feature of the Columbia Valley is the temperature.
Summer days are quite hot but the nights are cold.
According to Bob Betz, vice president of winemaking research for Stimson Lane, parent company of Chateau Ste. Michelle and Columbia Crest, daily temperature swings of 40 to 45 degrees between day and night are not uncommon toward the end of the growing season. Those cold nights preserve acidity in the grapes. Cold also describes Columbia Valley winters, when temperatures can dip as low as minus 12 degrees. That's cold enough to kill a grapevine.