Is it more likely lack of uv exposure or-40f weather that stops me from dropping fat in the winter? i can change lean mass extra activity adds weight

WINTER: We do not loss weight easily in winter due to lack of activity compared to summer months.

Lack of activity: Sounds as if those sub-zero temperatures may be discouraging you from much outside aerobic activity? If you can easily get to a mall you could try mall walking a few miles 3 or 4 times a week. Lower levels of activity should also warrant appropriate restrictions on your caloric intake during those winter months of inactivity. Yes, i know, not the suggestion you wanted to hear. Sorry.