Washington is the second largest wine producing state in the United States after California. It's located in the North West of the country and despite having one of the highest latitudes in the world amongst wine producing regions, much of it's climate is considered Continental Semi-Desert. This is due to the effect known as the Rain Shadow Effect, the effect of the Olympic and Cascade Mountain ranges combining to stop the clouds rolling in off of the Pacific Ocean and into the Eastern part of the state.
Most of Washington's wine comes from the East which has a long, dry, growing season, although small quantities are grown on West of the mountains in the state's wetter, cooler climate. On the East you can find the Columbia Valley, and within it lies the three major wine growing areas, the Columbia Valley AVA itself, Yakima Valley and Walla Walla Valley - each of which contain many AVAs as well as being AVAs in their own right.
There are many white grape varietals grown in Washington state today, chief among them Chardonnay, Pinot Gris, Sauvignon Blanc and Riesling. For the reds Cabernet Sauvignon, Merlot and Syrah lead the way in terms of planting.