I understand the "jet stream" to be a current of air high in atmosphere, similar to the North Atlantic current in the Atlantic Ocean. Apparantly, this air current is very strong and very fast, with the wind blowing at two hundred miles per hour or better.

But, why it would be displaced south as a result of global warming, and why that jet stream would bring colder weather at ground level is stuff I don't know and my expectation is that no one knows those things. If they did, the weathermen would be educating us about what's happening and why, but they don't seem to know anything about it.

It just goes to show that we have the potential to upset the delicate balance that is the climate of this planet without knowing where it will end up. So far as I know, no climatologists were forecasting that global warming would have any effect on the jet stream until movement of the jet stream further south during the winter became apparant. Then they made a connection, but that's hardly reassuring to those of us that presumed they knew what they're talking about when they forecast global warming. They seem to be as much spectators in this global warming spectacle as the rest of us.