A member in the NYC forum posted something about this a few years ago, forget who researched it, but anyway, they found that a warmer than normal Sept and Oct were nothing to worry about and many of them lead to a cold and snowy winter. It was when all 3 months (Sept, Oct, Nov) were warmer than normal that it became a huge problem. Nearly all of them lead to warmer than normal winter with below average snowfall in NYC, it was the kiss of death. Don’t know if the same holds true up there