I'm in southern California, so we most likely have a similar climate. We do occassionally get some surprisingly cold nights, and in really rainy years the constant wet can become an issue. Try to provide a dry place for the chickens to be in during the day to avoid foot problems. Don't forget dry nests! :)

Make sure there are no drafts in your coop and that it stays snug and dry. If you have more than two or three birds, they should do nicely if they are able to cuddle together. Birds with large combs can get frostbitten combs in really cold climates. If you worry about them getting enough warmth at night, install a light bulb in the coop to generate some heat. Make sure their food and water is kept clean and the food dry, maybe place a couple of bricks under the food & water dishes to raise them up out of the mud and keep them clean.

When I had only 5 or 6 birds, on nights when it was at or near freezing I'd go ahead and bring them into the house at night (doing this after dark was easy) and let them sleep on the kitchen floor.

One night during an especially heavy days-long rainstorm, we got a feeling around midnight that we should bring in the chickens. Their coop and the yard was ankle deep in water that we had to slog through to carry them into the house. We're talking thunder, lightening, slashing rain, howling winds--the works.

Not twenty minutes after that, a microburst ripped the entire roof off of our coop. We found it, mostly intact, two streets away. I have no doubt that it would have killed or severely injured all of our chickens had they been in there.

One of those 'Uh...what just happened?' moments!

Velvet ~:>

Make sure they have a sheltered, dry place to go that blocks the wind to cut the wind chill. As temperatures get colder, they will tend to eat a bit more to compensate, so watch their feed and fill the feeders a bit more often or a bit fuller so they don't run out.

Chickens are pretty resilient. The keys are the same as for humans and other animals--have a dry, wind-free, sheltered place to go.

When we had chickens, we had a converted building that was all windows on the south. The sun would shine in and warm the place up nicely during the day. If it was going to be 20 or 30 or so below 0, we would spread plenty of fresh straw on the floor that they could nest down in at night if they wanted instead of using the roosts. On those days, also, they typically wouldn't come outside the chicken house much. But once it started warming up again and we got up to 15 below or warmer during the day, they would head back outside.

We use a red heat lamp in our coop to give them warmth.
We put it on in the evening after they have all come in from free ranging during the day. Turn off the lamp as we let them out in the moring.
It can get below zero here for a week or more at a time.
So far we have only had two nights below zero.
I guess our girls are spoiled! LOL
Any farm supply store will sell the clip on lamp and red heat bulb. It is the same kind we use for our baby chicks.
inexpensive and supposedly keeps them laying longer... I haven;t found that to be the case....
oh well atleast we will not go out and find frozen chickens in the freezer, er, I mean coop! :-)