Here is a detailed article on the polar vortex, the current stratospheric warming, and the polar vortex split which has happened.
Following on from that some history of the effects of these events at the surface layer from previous years
And
Some model forecasts for countries most effected by this event in the coming weeks
It is a long and in depth article but take what you want
These guys publish such amazing detail. They leave no stone unturned.
Severe weather.eu
https://www.severe-weath...e-united-states-2021-fa/