Thankfulness is seasonal? Well, yes, actually. At least in my life.
The thankfulness season starts around Halloween/Reformation Day, and runs until January 1st. It encompasses "the holidays," as people call them these days--the holiday season.
Thanksgiving makes me thankful. My birthday, and my oldest son's birthday fall during this time. Christmas makes me thankful; my wife's birthday falls during that time as well.
The problem with all of this is something rather simple: a believer's life should be marked by thankfulness all the time. There is no season for thankfulness, any more than there is for joy, peace, patience, etc. Those are the fruit, and they should always be in season in our lives.
So how do we cultivate this? Well, I think a good first step is just thinking about it.
In Philippians, it talks about thinking on things that are true, pure, holy, and so on. I would add to that list things to be thankful about. Dwell on those things, and they will become a part of life.
So my challenge to you (and to me) is to make this season the start of a lifestyle of thankfulness. Thankfulness is something that's always in season.