All these photos are in my FLICKR photostream: https://www.flickr.com/photos/rosyfinch/
I guess it is a New Jersey thing. We said mild winter weather was shirt-sleeve weather (versus wearing a coat).
I checked Merriam-Webster.com and found this definition (my emphasis): shirtsleeve adjective \-ˌslēvz\\-ˌslēvd\
: not wearing a coat or jacket
: warm enough so that you do not need a coat or jacket: informal and direct
The Free Dictionary:
shirt·sleeve (shûrtslv)
n.
2. shirtsleeves The state of wearing no coat, jacket, or other outer garment over one's shirt: dined in shirtsleeves;
balmy weather that had them down to their shirtsleevesI think I was not supposed to use the hyphen