Don't take the weather bet. I just picked up a nice Eddie Bauer goose down parka on sale, and said "no way I going to need this thing this year"

it was 13F when I was waiting for the (late) train this morning.

Another thought is to find a rowing windbreaker - it's a short jacket with longer arms, and a panel that covers your backside. I've used mine with an underarmor long shirt and a thin fleece down to about 20-25, using pogies.