Columbia Plateau Climate: Hot Dry Summers, Cold Wet Winters

The Columbia Plateau (Washington, Oregon, Idaho) has a temperate continental (semi-arid) climate shaped by the Cascade rain shadow.

Key Characteristics

• Summer: Hot, dry. July avg 65–70°F (18–21°C); highs often 90–100°F. Rain shadow blocks Pacific moisture.
• Winter: Cold, wet. Jan avg 25–30°F (−4 to −1°C); snow common, rain at lower elevations.
• Precipitation: 10–20 in (25–50 cm) annually; 70% falls Nov–Mar.
• Temperature Swing: Large diurnal and seasonal ranges.

Why So Dry?

The Cascade Range forces moist Pacific air upward—cooling, condensing, dropping rain/snow on western slopes. Descending air warms adiabatically, creating a rain shadow over the plateau.

Agriculture & Life

• Irrigation (Columbia/Snake Rivers) enables wheat, apples, potatoes, vineyards.
• Dryland farming (wheat-fallow) in wetter margins.
• Wind, dust storms, wildfire risk in summer.

The plateau's climate is a textbook rain shadow—productive with water, harsh without.