The ensembles picked up on the pattern change mid December and of course were about 7ish days too early with it. They all had a system rolling through mid month, with another on its heals 4-6 days later. As it got closer the gfs was the first to suggest it, but I'm not sure what day that was. The euro hinted not long after. The gfs lost it, the euro picked it up, the gfs has corrected back and here we are