A good rule of thumb is that if you can't find a single season over like a 100 year sample size worth of data that meets your criteria, then it may be too exclusive, but to each their own. Maybe you could at least split your "central based" composite into a couple of subsets because there is most certain a difference between an eastward leaning central based season, like 2010-2011, and a season that I consider to be west based, like 2011-2012. That needs to be reflected IMHO.