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Columbia Plateau Climate

The Cascade Mountains cast a long rain shadow over the Columbia Plateau. In the state’s semi-arid interior, summers are hot and dry and winters are cold and gray.

Precipitation occurs mainly between late fall and early spring. Annual averages vary from six inches along the Columbia River near Hanford Reach to 25 inches in the Palouse Hills on the ecoregion’s eastern edge. Snow falls in the ecoregion, though it rarely lasts long before melting.

With its low elevations, and a moderating maritime effect, annual temperatures average 40 to 57 degrees, though extremes can range from subzero to over 100 degrees. Drought and fire are not uncommon.


For details of this ecoregion within Washington, click a subheading in the left column.

View the more general description of this ecoregion in North America

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