Very interesting read! A question regarding the shape of the polar vortex:

This winter is obviously proving me wrong, but I thought that a strong polar vortex typically was correlated to a round polar vortex. Does the shape of the PV not really give any good indication of it being strong or not? And could you say anything about how a stretched, strong PV typically could play out for Norhtern Europe/Scandinavia, compared to a round, strong PV?