It could be rainy in the coastal areas in January, but one never knows -- last year there was almost no rain at all. Otherwise, driving around Ventura and most of SoCal in the winter is just like the summer. Lots of cars, but clear and dry roads. There is sometimes snow in the mountains over 6000 feet.
And here is a link to statistical climate info about 29 Palms, next to Joshua Tree:
Weatherspark siteIf you will be in Joshua Tree on the night of Jan 3-Jan 4, try to get outside before dawn to watch the meteor shower. Bundle up!!
Weatherspark is a really useful site when you are planning a trip.
2012 Fun Finder X-139 "Boondock Style" (axle-flipped and extra insulation)
2013 Toyota Tacoma Off-Road (semi-beefy tires and components)
Our trips -- pix and textAbout our trailer"A journey of a thousand miles begins with a single list."