A typical July day here in Berkeley

© MMIX Earth Environment Service (annotated by me)

Folks are often perplexed by our local ocean fog. Even though it is easy to conceive that it has evil intent (we just saw it stay offshore until just before 4th of July fireworks were scheduled to go off, where it rushed onshore!), it happens for reasons that are pretty easy to understand.

The Pacific Ocean is a relatively cool body of water, which moderates our coastal environment, keeping it from becoming too hot in summer as well as too cold in winter. Our interior valleys, far from this influence, do experience much warm summer temps (and colder winter lows). As this warm interior air rises (orange arrows), it creates a vacuum that pulls in air from surrounding regions. Often this replacement air comes from the coast, pulling the ocean fog (created by the cooler ocean) along with it (blue arrows).

Sights of fog spilling over our coastal hills are very familiar to long time residents. Sometimes when a warm inversion layer holds the fog down, this cool air can only come in through the lowest points. The main 'low point' along this part of California coast is the Golden Gate, which is why it is so picturesquely half-shrouded in fog. Where does the fog go as it spills through this opening? First stop is Berkeley, where we live! I work in Oakland, which often warms up during the day in July, but back home in Berkeley, the fog can sit all day. My tomatoes are not particularly happy right now, and the rose is developing mildew, and many other warm-loving plants are in a sort of suspended animation, waiting for the occasional warmer day. But those that DON'T like the heat are enjoying a longer season that otherwise!