When you visit Ventura, especially if you are going to visit the beach areas and downtown make sure you bring a sweater or jacket.
California's main form of weather is wind. Usually in the afternoons the ocean breezes pick up and sometimes can be quite 'stiff." You can start out in the morning with a gentle breeze and by 4 PM you are shivering due to strong on-shore winds.
Fog is another factor to watch out for, espcially in the summer months. It can quickly roll in and change the entire region's temperature in a matter of minutes.
Generally speaking the fog stays near the coast so if you travel inland to areas like Ojai or Santa Paula the weather is warmer and not foggy.
These are ridiculous (and illegal in my state), but here they're all over the place. I didn't see any in the center of town, but as you move southward or eastward, you start seeing them a lot more frequently. Careful about running the lights, even if there's no one there.
Don't get too close to the edge of the cliffs because the ground is unstable and it's also windy. Both factors could cause one to fall over.