The only places you will find a theme park that is actually open during the Winter is in Orlando, Florida or in Southern California. San Diego is home to Legoland, CA, which happens to be where I work. There's also SeaWorld San Diego and Belmont Park. If You go north to Los Angeles, SFMM, Disneyland and Knott's Berry Farm are very close to each other. Except for Six Flags, most parks are usually open everyday. LLC is closed Tuesdays and Wednesdays during the offseason. January is definetely the best time to go to any park in SoCal.