When it is cold outside, the only acceptable outerwear with a suit is an overcoat. But there are a lot of terms thrown around when discussing these dressier jackets.
Ulster, guard coat, chesterfield, covert, polo... so many choices. I'm probably unduly influenced by John Constantine, but in my mind, the urban working coat is the trench coat, period.
I wish I had managed to hold on to my Navy greatcoat (water damaged during a flood, unfortunately). That was probably the warmest cold-weather coat I've ever owned, and it looked good, to boot.