It can get really cold. The coldest I have ever been at
Disneyland was in MAY one year, during a crazy windy, drizzly night. I literally wished I had a winter coat and gloves. It was in the low 50s that night. It had been in the 80s during the day.
Lately it's also been in the 40s at night here, but that's typical for January. One thing you need to remember is that often the humidity here is very low and that makes it feel much colder than it actually is. You *should* be fine with jeans and sweatshirts, but you need to check the forecast a few days out to know for sure.