Not sure it is only a southern thing. I worked in the southern hu desert of California. When i got to work some mornings there would be icicles hanging from the eaves. Shorts hoodie and a jacket to start, but by lunch break i would be in shorts and tank top.Well I'm pretty far south and around here only the teenage girls wear that odd outfit.
They usually wear socks and sandals too. I've done that one a couple time tho