Looks, in fact, like Sudden Stratospheric Warming (SSW) followed by Negative Arctic Oscillation and Arctic Vortex Collapse. As NOAA’s BEST scientists modeled it before the furlough, and I Really Appreciate Science confirmed.
You can compare the fronts and both High (H) and Low (L). Remember in the Northern Hemisphere use your Right-Hand with “Right-Hand Rule” when we discussed The September or Fall Equinox ? In the WRF calculations below, you can see that in the last hours, the apparent “mad rush” of cold air across the Canadian Border towards the Dakotas in the far right. That is the result of Vortex collapse and Negative Arctic Oscillations. Very dramatic and quick, isn’t it?