We tend to think of Washington and Oregon together, but the wine climates for the two states could not be more different. Even though Washington is further north than Oregon, the climate in its main wine producing regions is hotter than Oregon.
As the topographical map of the two states indicates, the difference lies in the configuration of mountain ranges. In Oregon, a relatively low coastal range protects the interior from the worst of the Pacific chill. Some cool air does flow into the interior valley over the tops of the coastal range and through several gaps, supporting the cool climate wine region of the Willamette Valley. The Washington coast lacks a protecting coastal range, making western Washington too cold and wet for fine wine grapes (although there are wineries and tasting rooms in this populous region).
Further inland, the high Cascades act as a near total rain shadow in both states. The eastern side of the Cascades is arid, but irrigated, in both states, by water from the mighty Columbia River. Washington’s main wine growing appellations are here. Several of them edge over onto the Oregon side of the Columbia.