I was waiting to see what others have said, because I am in California as well. I would assume we are not stable enough as it can get hot real fast, then cold and significantly different from the natural habitat. I would be concerned when our weather goes into the 90F or more, then how would you cool them, unless you can run cool misters based on a thermostat? Then when the coldest months, you have to create heat.
Seems like a solarium or greenhouse with temperature regulation would be the closet to outdoors I would try and am considering the costs of those options myself.
I'm in Miami (so not the same, I know) but I've had all three melleri outside for months now, since about Feb/March, and they've all been doing super well outside. Especially my newest WC, who I purchased the previous October, has been doing so much better outside than he ever was indoors. His colors are phenomenal all the time, he's content, has a great appetite, and isn't nearly as stressed.
So yes it gets hot but between regular misting outside and lots of shade throughout most of the day they appear to be thriving. Although here in Florida summer is not just hot season but rainy season too, so it's raining most evenings. I don't know what the weather is like all summer in your area but here it cools off and rains pretty often.
I do remember Cheryl Dewitt kept a lot Jackson's in Del Mar, Ca a long time ago. She was in a coastal somewhat lagoon/marsh area that found unusual humidity and temp stability not typical to the rest of San Diego County. Seems like the melleri confirmed locals are in either these type of coastal areas or higher elevation.
So I think we are close if using a green house that allows UVB, that can set a max/min temp and simulate rain well to get enough water. Be nice to see what other have done.
I do know that there are invasive colonies of Jackson's chameleons and Veiled chameleon's in California that are thriving.
I think that as long as there is extremely ample shade, as well as misting several times a day, we should be good. I think the best way to do this would be to hook up a couple of misting nozzles throughout the enclosure and have them running every couple of hours at least.
Any and all responses are welcomed and GREATLY appreciated!