Added thought — Cars don’t expect to see runners out when 98% are hiding indoors. I always bring lights, blinkers, etc. There are some really good LED wrist flashers, headlamps, etc. that run forever on 2AAA batteries and cost very little but make it easier to notice me.

YMMV — Your mileage may vary. As I have gotten older (and slower), I need more clothes. Also, once ice hits and you add spikes to your shoes and layers of clothes, you also slow down. This means experience counts for more than a guide based on average runner and assumption that temperature v. clothing is a linear…