Why Is the Eastern Part of Washington State So Dry and Western Washington So Wet?

Weather on the western side of Washington is wet and quite warm, considering its northern latitude.

For example, in January, on average, Seattle has a mean temperature of 41° Fahrenheit and receives 5 inches (12.7 cm) of rain.

Spokane, just 282 miles (454 km) east and at about the same latitude, on average has a January temperature of 26° Fahrenheit and gets 1.8 inches (4.6 cm) of rain.

There are two reasons for this difference in climate.

Western Washington lies next to the Pacific Ocean, which keeps it surrounded much of the year with warm, moist air.

Second, the Cascades Mountain range blocks much of that moisture from reaching the eastern part of the state, a weather phenomenon called the rain shadow effect.

In fact, before irrigation made eastern Washington a productive farming area, the land was almost desert-like.

Oregon’s two climatic regions are similar to Washington’s, for the same reasons.

Washington produces more apples and pears than any other state.

Farmers in the central part of the state also grow much of the nation’s berries, cherries, grapes, and plums.

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