Here in Wisconsin if it is in the mid 30s with no wind many people will go without a jacket.
I work outside in a t shirt and light long sleeve shirt (to protect my arms from splinters) when it is in the low twenties as long as the wind isn’t blowing.
I was out and about tonight, running errands in a t shirt with an unbuttoned long sleeve shirt over it. Snowing, maybe 25 or so, didn’t bother to check. Only reason I wore the longer shirt was to conceal the Glock on my hip. Wasn’t all just dashing from car to store either. Stopped and helped dig out and push out a couple of stuck motorists too. I did put on gloves for that.
Yup. If its not too long outside.