San Francisco's cooler summers result from the California Current, which brings cold ocean air to the coast.

San Francisco enjoys cooler summer temperatures due to the California Current, a cold ocean current flowing southward along the West Coast. This current cools the ocean air, which is then carried inland by coastal breezes, moderating temperatures in coastal cities like San Francisco. This effect, often accompanied by a marine layer of fog, keeps San Francisco’s summer days mild and prevents the intense heat felt in inland California areas. This unique cooling influence not only affects daily temperatures but also shapes the city’s iconic foggy mornings and creates a comfortable, temperate summer climate.