The northern part of MN and the NE half of NoDak are both north of the Laurentian Divide. Water flows north 'above' it. (The 'Divide' splits 3 watersheds at onc

The northern part of MN and the NE half of NoDak are both north of the Laurentian Divide. Water flows north 'above' it. (The 'Divide' splits 3 watersheds at once near Hibbing, MN.) [https://en.wikipedia.org/wiki/File:NorthAmerica-WaterDivides.png https://en.wikipedia.org/wiki/File:NorthAmerica-WaterDivides...] The land between the Arctic and the Divide is still quite flat as a result of the last glaciation (it filled up with meltwater for a few thousand years). There isn't much topography to slow the cold air down. Cities north of that green-line have historically been the coldest.