How cold is it in South Dakota in April? What clothes do I need?

How cold is it in South Dakota in April? What clothes do I need? I've lived in CA all my life and am going to be spending some time in SD but I'm not sure how cold things are that time of year. I'm guessing it's not below 0's but still colder then I'm used to. Would I just need a warm jacket or something or full blown scarves and mittens?