California Central Valley Climate: Mediterranean—Hot Summers, Wet Winters

The Central Valley's climate is Mediterranean (Csa/Csb Köppen): hot, dry summers; cool, wet winters. But "Central Valley" spans 450 miles—microclimates matter.

Summer (Jun–Sep)

• Highs: 95–105°F (35–41°C) routine. 110°F+ spikes (esp. south: Bakersfield, Fresno).
• Lows: 60–70°F. Radiational cooling—clear, dry nights.
• Rain: Near zero. June–Sep < 0.1".
• Air quality: Ozone, PM2.5 trap in bowl. Worst in nation some days.

Winter (Nov–Mar)

• Highs: 50–60°F (10–16°C).
• Lows: 35–45°F. Freezing nights (28–32°F) common Dec–Jan. Tule fog (dense, ground-hugging) Dec–Feb—visibility < 100 ft, lasts days.
• Rain: 8–12" annual (north) to 5–8" (south). 80% falls Nov–Mar. Atmospheric rivers = flood risk.

Spring / Fall

• Transition seasons. Wildflower blooms (Feb–Apr) if winter wet. Wind events (Diablo/Montezuma) drive fire risk.

North vs. South Gradient

Agricultural Engine

This climate + Class 1 soils + imported water (CVP, SWP) = world's most productive agricultural valley. 250+ crops. $50B+ farm gate. But climate change: less snowpack, more heat extremes, SGMA groundwater law forcing fallowing.

Mediterranean on steroids: the dry is drier, the hot is hotter, the water is imported.