40 is a tricky temperature. It can be a little warm for a lot of jackets, but too cold for just a long sleeve jersey. Depending on your tolerance for cold you may be able to get away with a mid-weight base layer and a long sleeve jersey.

I use a PI Gavia jacket that works wonderfully for me. I need to unzip the front a bit when temperatures get into the upper 30s. Unfortunately, PI doesn't make this jacket any more (not sure what the equivalent would be in their current line).

paul