i'm 100% the same as far as weight gain / loss!
In the winter when it's colder and dark out early I love to go to workout classes 6-7 times a week where it's hot, high energy and I release a ton of endorphins. I probably lose somewhere between 10 - 15 pounds of fat and add 5 pounds of muscle.
In the summer, I like to be by the pool, eating lobster rolls and drinking fun drinks / wine. My 3-4 mile maintenance runs aren't quite as effective, or frequent.