So far this year, we have seen the polar vortex break apart in the middle part of the stratosphere as a result of more than a few sudden stratospheric warmings. However, the opposite can also happen- sudden stratospheric coolings, while not called that specific name, do occur. One can observe significant cooling in a very short amount of time in a very similar situation that sudden stratospheric warmings occur.
If the polar vortex were to rebuild in the higher levels of the stratosphere, it actually would not be as significant as you may think. The stratosphere has its strongest effect in the lower levels, closer to the troposphere. If we were to see a strong rebuilding of the polar vortex in the lower levels of the stratosphere, I would be much more concerned. However, the forecast is calling for a very disorganized vortex in the middle stratosphere, with strong rebuilding seeming to be held to the upper stratosphere.
And the fact of the matter is, this is 384 hours out. So many things can and will change- it is very possible the polar vortex may weaken rather than strengthen. However, this forecast of a rebuilding has been coming back for multiple runs of the GFS, and trends are always key when looking for a forecast that has the best chance of verifying.
So keep your eyes on the models, but unless the polar vortex rebuilds at the 100 millibar level, the 1 millibar level is really nothing to write home about.