Arctic air coming in for another visit: Let's enjoy today and early tomorrow as much as we can because that unwanted relative from the north is coming in for another visit.
You can actually see the mild air coming for a visit today with 850 mb temperatures near +3! Okay, so here's the other shoe...and it's big one. This usually happens ahead of an arctic weather system as that gateway to the north will be opened by another 'clipper' type weather system moves through the area and changes the flow to a north flow which opens up that arctic gateway.
You can see the cusp of the cold air moving in late Friday behind the clipper system with temperatures of -14 to -22 Celsius coming into northern Indiana by Friday evening.
It's not the core of the coldest air but it is certainly formidable as the coldest air (-50 C) sits in southern Canada and northern Michigan. But a couple of things really don't bode well for a quick moderation in temperatures. One is that the cold air is moving across an area which snow covers the ground. That makes it nearly impossible to moderate temperatures. The other is that the core of cold air is not far from the air mass we will be experiencing.