Why San Diego Is Warmer Than Seattle: Latitude, Ocean, Winds & Topography

San Diego (32.7°N) and Seattle (47.6°N) sit 1,650 km (1,025 mi) apart in latitude — but their climate divergence goes far beyond latitude alone.

1. Latitude & Solar Angle

San Diego receives ~30% more annual solar energy. Lower sun angle in Seattle spreads radiation over larger area; shorter winter days (8.5 hrs vs 10 hrs). Fundamental driver.

2. Ocean Current Regimes

• San Diego: California Current (cold, southward) — but coastal upwelling brings cold water; yet air masses modify over land
• Seattle: North Pacific Current (cool) → but Puget Sound geometry traps marine air; less continental influence

Paradox: Both have cold currents, but San Diego's coastal plain allows daytime heating; Seattle's topography traps cool marine layer.

3. Prevailing Wind Patterns

• San Diego: Subtropical high dominates — offshore flow (Santa Ana) brings hot, dry desert air; onshore flow = mild marine
• Seattle: Westerlies off Pacific — constant cool, moist marine inflow; polar jet dips south in winter

4. Topographic Shielding

• San Diego: Coastal mountains (Cuyamaca, Laguna) block some marine layer; inland valleys heat rapidly
• Seattle: Olympics (west) block nothing — marine air flows straight through Chehalis Gap; Cascades (east) trap systems

5. Air Mass Source Regions

• San Diego: Tropical/subtropical (Pacific high, monsoon remnants, Santa Ana)
• Seattle: Maritime polar (Gulf of Alaska, North Pacific) — cool, moist year-round

Climate Data Comparison

Summary: Latitude sets baseline; ocean currents, wind patterns, topography, and air mass origins amplify San Diego's warmth and Seattle's cool moderation.