Is The Jet Stream Causing More Extreme Weather?

Stuart Staniford:

If you click on my screenshot above you'll get the Wiki video in a separate window and I highly recommend going through it a couple of times.  You'll notice that the jet streams have big chaotic-looking meanders in - the one in the screenshot above is about the size of North America, and that the meanders progress in a generally westward direction.  These are called Rossby waves (also known as planetary waves).

These things have a massive effect on the weather.  If you think of the jet stream as being at the boundary of the polar cell and the Ferrel cell, it should be clear that when a big loop is south over your location, it's likely to be cold, whereas when you are in a northward tongue with the jet stream well north of you, it's going to be warmer.  Similarly, since it's the mid latitudes where the regular pattern of cyclonic storms dominate the weather, the Rossby waves have a lot to do with where the storm tracks go and thus where it's wet and where it's dry.

As the Rossby waves are slow - often taking a week to cross the US - they have a lot to do with the persistence of the weather - the fact that things are often nice for a few days or a week, and then wet and miserable for a few days at a time.  Indeed, anomalies in the jet streams can cause much longer patterns - sometimes a meander will become detached from the main course of the jet stream and just kind of hang around (one kind of what is referred to as atmospheric blocking) leading to weather that may not change for weeks or longer.

Above my pay grade, but it definitely would have a big impact on agriculture.