Is packing on the pounds in the winter time normal?

I have a male cat that is outdoors and indoors. He spends his days in and out but his nights mainly inside. I have noticed that since it has gotten cold hes starting to pack on the pounds. He is also not fixed. But I have not had any problems with him spraying in the house and if he has to go he uses the little box or prefers the outside. I have been feeding him a mix of Pro Plan normal which I had a free coupon for and Purina Naturals. I have a dye allergy so I can't feed him the too cheap of stuff. He doesn't get much wet food, I do occasionally maybe once a week feed him some sweet potato or some pumpkin. He currently weighs 15 lbs. I was wondering if this is normal. He feels heavy but also muscular if that makes any sense. Any tips would be nice thanks. View media item 247671

Normal weight for a cat varies depending on breeding or the genes they inherited.   There are varieties of cats where males do get upwards of 18 lbs.   Usually the practise is to note if you see a `waist` line while looking from above.   This is what normal should look like - or close to it anyway.



http://www.catinfo.org/?link=felineobesity

Thank you very much. I will try to take a post of him like that. He still has the energy to spurt like a rocket and he still climbs all over outside. He almost like a squirrel jumping sometimes. It makes me wonder what breed he is part of since he's always been a high energy cat. Not as much in the winter. But he hates getting his paws wet. So he'd rather sleep eat drink and then go outside for a little while.