I'm almost positive that I've read about hormonal response to seasons/daylight. I'll have to dig for the study/paper later

I've found ample time in the sun keeps my energy up and hunger down.

We can presume that the evolutionary basis is to give us padding for surviving winter. My N=1 however has significant muscle gain right now with no appreciable fat gain...

I have noticed my appetite ramp up big time for the last month or two. To the point for a while there I kept falling off the wagon because I continued to think I needed my 'spring' level of calories (and carbs for that matter).

I've upped the fruit and starchy veg and this has helped enormously with cravings. I'm about 7lb heavier than I'd like to be at the moment but it's small potatoes compared to the 60lb heavier that I used to be.

Actually, I thought it was common knowledge that everyone tended to gain in winter and lose in summer. But come to think of it, I have never looked for any research papers on it.

From an evolutionary standpoint, it would make sense for hormones to direct the body to store more fat before winter. It was even more difficult to find food in the winter in most regions, so the genes that survived through the generations were the ones successful at storing enough extra energy in the late fall to ensure that the body would be able to survive long periods of little or no food.

But your issue appears to be opposite this logic. You gain in the summer and lose in the winter. It could just be the way you're built. Everyone is a little different, and the hormones of one person can differ greatly from the hormones of other people.

I recall reading that your metabolism is slower in the summer months, and faster in the winter months. It slows down in summer because that is when food is aplenty, and we need to store it away for the winter. In winter, we are colder, and we our basal metabolic rate goes up just to keep us warmer.

The reason that, in current society, we tend to gain weight in winter is because we get a lot less movement (not as nice outside, too cold, tend to not go out as much), and because winter foods are much more dense in calories. Think about it, it is a time much more devoted to desserts (pumpkin pie, halloween candy, christmas cookies, etc).