There is a large fog bank that hangs off the coast of California that meteorologists call the marine layer. Often in the summer, the pattern is for hot air to rise in inland valleys. Cooler air from offshore rushes in to replace it, and often brings some fog with it. This cool onshore breeze is our natural air conditioner, and it switched on nicely today. I actually needed a jacket on my ride.
The fog was breaking up a bit after 10:00 am, but there was still a cool breeze