This sudden stratospheric warming (SSW) was predicted a while in advance by The Weather Centre, but the magnitude of this warming was severely underestimated. Records have been shattered across the board, especially at the 70 millibar level, as shown above. The red line of observed temperatures has passed above the thin gray line, which is the record stratospheric temperature for that day. It is safe to say this winter will go down as a historic one, as far as the stratosphere goes.
So we have a very much historic SSW happening. As I have explained, there is a 2-4 week lag between the warming event and cold weather reaching the surface. If we saw a record-breaking warming like this, one can only imagine the potential there is for severe cold to hit the United States. The reason I say potential is because the cold's path will be determined by the atmospheric pattern at the time, something that will take another several days to determine.