We played this same game last year where January decided to show up later in the month after a mild start. We’ve seen signs for a few weeks that our days in the mild pattern were becoming limited as the cold has been building for quite some time in Canada. As of today:

The storm system that will develop Friday and swing through the Great Lakes will be the mechanism that pulls the cold air down into lower 48 and several storm systems thereafter will likely help to keep it locked in place across the eastern US. The “switch” will be flipped. Anything pink is below freezing: