Went 3 years ago about this same time. No crowds but lots of rain! It was raining the whole week we were there! Also it's the rainy seaon for southern Cali.
We've visited during January the last three years. The first year it was a mix of rain and sunshine, the next it rained the ENTIRE time, and last year there was all sunshine and 70 degree days. Good news is we had a great time every trip!
I was there around that time this year and there were no crowds and the weather was next to perfect! No rain and it was quite sunny surprisingly. It was cooler at night but maybe we just lucked out with there being no rain.
We were in Disneyland the last week of January this year and the weather was just beautiful, sunny, clear and highs in the 70's. The evenings did get a little chilly, enough so that a light jacket was needed. We had a wonderful time.