It's not surprising, most of us gain weight in the winter months right? It's cold, we can't get out much, there are fewer hours of daylight. I've also read that lack of sunlight contributes to the effects of depression which plays a role in weight management.
If you're outside you're walking, you're at a party and being social, you're enjoying nice weather, you're probably not sitting around watching tv so you're most likely engaging in a healthful activity.
Sunlight is very important to me. I practice my chi gong first thing in the morning facing the sun and absorbing its energy.
“If you try to lose weight by shaming, depriving and fearing yourself, you will end up shamed, deprived, and afraid.” Geneen Roth