I wear mine from 2-13 C with just a t shirt underneath. (I’m an F guy but think I got that range right. Basically, 36-55 F). It can be worn in lower temps with a flannel but I switch to my N1 so I can pop the collar and keep my neck warm, especially if windy.
I love this jacket so much, I bought the green serge one too. I actually wear that one more due to the longer sleeves, but this one is more subtle and can be worn with anything. They are both awesome.