This is one of those 'chicken or the egg' questions. I think it's at least partly the case that it's the jet stream buckling that creates the warm air advection: it has been the stalling low pressures that have driven the warm air north on their eastern flank. The question, I think, is for how long that upper block then influences the jet stream pattern because we've all seen situations where the block is driven aside by a strong surge of the jet.
Originally Posted by: Gandalf The White