"It is cold at night."
Difference between Samui vs Tsumetai http://yesjapan.com/YJ6/question/623/can-you-tell-me-the-difference-between-tsumetai-and-samui
さむい is an adjective, さむく is the adverb form (also used with the negative form).
I think the latter is used when it's going to be negative like さむくない & the former for anything else, basically
Why is there a は after よる when "It is cold at night", but not after it when "It rains at night?"
Is 夜 (よる) Hi-Lo or Lo-Hi? I always thought it to be よる／. Though it is pronounced よる＼ in this example. I know it doesn't really matter except to sound more natural but that's important to me.
I think my textbook one of my textbooks says it is regionally different so it's best to ignore it at the moment.