If you look at in the simplest term anything that disrupts the usual winter pattern over the Polar region can only have the potential to alter the synoptic patterns below.
Nothing guarantees a severe cold spell but as that tweet says, we have got the jet on a more southerly track and that has produced some wintry weather, particularly further north. That pattern is set to repeat itself again from Friday and through the weekend, with cold conditions spreading south and more chances for snow.
Don't forget that we are also at the point in the solar cycle (sunspots) when blocked periods in winter are more likely but, just like a SSW, that doesn't guarantee it will happen.
Originally Posted by: Gandalf The White