If you're planning a California wedding during June-September it's safe to say that the little weather diagram will show nothing but sun. But if you're planning your wedding during the other 8 months I highly recommend using The Weather Channel's 'HOURLY' guide the day before and the day of your wedding. Just type in the city or zip code and hit the "Hourly" tab. This handy tool won't allow you to plan 2 weeks out, for instance if you have to order a tent, but it will help you schedule your important plans that can accommodate last minute changes, for instance help you decide on whether the cocktail hour should stay outside or move inside. I use this site A LOT during these possibly wet months and work with my couples to plan out the best time for outdoor portraits. For instance the original time-line might have portraits at dusk, but if rain is scheduled to start at sunset, we might change the portraits to precede the ceremony.
I've found this site in particular (not Google and not Yahoo) to be highly accurate! So don't let the unchangeable weather set the tone of your mood, just use this site to maximize the positive.
The Weather Channel (www.weather.com)