Washington Wine - Geography and Climate

Geography and Climate

The Cascade Mountain range is a defining feature in both the geography and climate of Washington state. It serves as a dividing line between the wet, marine influenced climate of the western part of the state from the drier, desert-like climate of the eastern half. The mountains themselves create a rain shadow over the eastern half by blocking weather fronts holding precipitation from carrying over the mountains and descending onto the Columbia River Basin. This creates the arid desert-like conditions with a more continental climate in Eastern Washington and heightens the roles of rivers—most notably the Walla Walla, Yakima, Snake and Columbia River—in the region's viticulture. In addition to providing vital irrigation sources, the rivers also help to moderate temperatures during the winter which is prone to severe frost and freeze coming from the Arctic. In winter, overnight temperatures in the wine growing regions of Eastern Washington can drop to as low as −15 °F (−26 °C). The sudden drop to these sub-zero temperatures can make the water in a vine's wood canopy quickly freeze which can cause the vine to literally burst open. The severity of these conditions can wreak havoc on a year's harvest, as was the case in the Walla Walla AVA with the big winter freezes of 1996 and 2003.

The geological history of the state can be traced to the movement of glaciers along the edge of the Pacific Northwestern section of the North American Plate that retreated from the area over 16,000 years ago, leaving behind a free-draining gravel bed up to 250 feet (76 m) deep in some places. The Great Missoula Floods at the end of Ice Age created much of the Columbia River basin and brought soil deposits to the region from as far away as modern day Montana. These floods released a torrential wave of water (nearly equal to the amount of water in Lake Ontario and Lake Erie combined) traveling more than 60 miles per hour (97 km/h) and 500 feet (150 m) high across the Columbia Plateau. These floods carved out the geographical landscape of the region, creating coulees and gravel bars as well as depositing layers of gravels, sands and silt that would eventually mix with loess and volcanic dust.

Today the topsoil found throughout the Columbia Valley is mostly sandy and stone-studded on top of basalt-based soil foundation created by persistent lava. These sandy loam vineyard soils create a nearly inhospitable environment for the phylloxera louse, which may be one of the reasons why the phylloxera epidemic has not ravaged the Washington wine industry as it has the Californian and French wine industries in the past. The state's northerly location above the 46th parallel north allows Washington's major wine growing regions to experience 17 hours of sunlight in the summer—two more hours of sunlight during the peak of growing season than what California sees further south. During the growing season Eastern Washington experiences a wide diurnal temperature variation (up to 40 °F (4.4 °C) difference between daytime highs and nighttime lows) which allows the fruit to fully ripen while the cool nights help the vines to shut down, allowing the grape to maintain natural levels of acidity.