Characterized as a warm, semi-arid, continental climate, Walla Walla Valley produces red wine varieties that love the sun but can handle a cold winter.
Average temperature from April 1–Oct 31 is 63.5° F (17.5°C).
Continental climates tend to have significant variation in temperature (hot summers and cold winters) and prevailing overland winds. Temperatures are not moderated by bodies of water.
Average annual rainfall is 15 inches (381 m) with just 9 inches on the western side of Walla Walla Valley and 22 inches on the eastern side.
Walla Walla Valley's climate is designed for robust red wine varieties.
There is no lack of sunlight and warm temperatures during the growing season in Walla Walla Valley. Thus, it makes a great spot to grow bolder wine varieties like Cabernet Sauvignon, Syrah, or Tempranillo.
However, winters here are frigid. Every 10 years or so a deep freeze sweeps through the valley that kills vines back to the roots. It's so bad that in some areas vintners bury a cane each year as "insurance." This way, when the freeze kills upper vines, they just dig up the one they buried to grow grapes.
Managing sun helps maintain acidity and alcohol levels.
Too much sun and heat during the growing season causes grapes to become shriveled and overly sweet before the seeds fully ripen. This makes for unbalanced wines with bitter tannins, high alcohol, and low acidity.
In order to manage this, some producers practice spacing their vines closer together so that each row shades the next. By creating a great deal of natural shade, only the vines on the southern edge get toasty.
Dry farming is difficult in the Walla Walla Valley.
The western half of Walla Walla Valley receives only 8 inches (203mm) of rain a year. For perspective, that's less than the Gobi Desert! This means most of the vineyards in Walla Walla Valley are irrigated.
As you move eastward in the valley, rainfall increases up to 22 inches (559mm) of rain, which is nearly enough to dry farm! A few winegrowers in the Mill Creek area and other western forked canyons get enough rain to dry farm.