My daughter's best friend was diagnosed with MS at 11 and they live in Northern California, what's considered part of the "North Bay" of San Francisco, Sonoma county.
I've lived or driven through a vast majority of California (except the very northern part) and the temps can vary DRASTICALLY depending on where you're at at any given moment.
The central valley (where redding, chico and red bluff are) is EXTREMELY hot during the summer. Temperatures in the 105 to 120 range are the norm, not the exception, although it is very dry. It does tend to rain a lot during the winters too.
The mountain communities are just that mountain communities. It tends not to get too hot, but gets cold and snowy in the winter, depending on how high you are. Although no where NEAR what you're used to in Alaska LOL Would probably seem balmy to you LOL Donner Pass (after the Donner party) is in the mountains of CA ... so there ya go :)
Along the beaches in southern ca it's almost perfect most of the time but can get chilly, foggy and damp during the winter. the beaches in northern ca it's chilly and damp a lot of the time. When we lived in Sonoma county our kids had field trips to Bodega Bay on a yearly basis it felt like. There was more than one year where a nice warm coat, gloves and ear muffs would have been a joy to have at the beach ..,. IN MAY. And yeah you can swim in the ocean in southern ca and not so much in northern ca.
My favorite place to live temperature wise has been Sonoma county. It's pretty temperate most of the year. With temps getting up over 100 only occasionally. You have tons of stuff to do, you're an hour from San Francisco, a couple of hours from the mountains and skiing. Winter time daytime highs in sonoma county hover around the 70 degree mark (give or take 5 degrees or so) and does get lots of rain during the winter. Summer time highs hover around the 85 degree mark (with some spikes now and then), in fact a lot of houses in Sonoma county don't have A/C, although most newer ones do, because it doesn't get too hot most of the time. And even when it does get hot during the day the temps drop DRASTICALLY at night so sleeping is easy and comfortable without A/C. I slept with a relatively heavy comforter at night a good portion of the time I lived in Sonoma County :)
My second favorite place in California is San Diego. The temperatures are relatively stable most of the year and it's just plain BEAUTIFUL down there. And the water can be swum in a good portion of the year. I've never lived in San diego tho, just been there several times. I did live in Orange county (think disneyland area) and it was pleasant weather wise but had more 90-100 degree days.
I can say of all the places I've lived in Ca that except for San Francisco (I actually lived IN the city) ... I was able to wear shorts and a t-shirt at least 80% of the year and be completely comfortable. During the winters sometimes I had to go to Jeans and a t-shirt, and very occasionally I had to put on a jacket, sweater or sweatshirt :)
Ok this has gotten REALLY long LOL If I can be of anymore help please let me know.