I think its worh noting that the Weather Network is the source for this article about a new study that establishes a strong link between an increase in extreme weather events and Global Warming.
Researchers link extreme weather events to global warming in new study
By Scott Sutherland
The pattern of the 'planetary waves' that are created in the flow of the jet stream are largely dependent on the difference in temperatures between the equator and the north pole. If the temperature difference is large (hot at the equator and cold at the pole), the polar vortex is relatively strong and the waves are fairly small, as shown below (from early in the animation).
In this case, the waves tend to move along at a fairly good pace, and thus the weather conditions change fairly quickly as well, and no particular area gets trapped under extreme conditions for long periods of time. However, if the temperature difference between equator and pole is smaller (hot equator and cool or warm polar region), the polar vortex weakens, waves can become quite large, dipping far to the south and stretching far to the north - like in the snapshot below - and the overall movement of the waves slows down at the same time.
"Behind this, there is a subtle resonance mechanism that traps waves in the mid-latitudes and amplifies them strongly," said Stefan Rahmstorf, a researcher at the Potsdam Institute for Climate Impact Research who co-authored a new study investigating these waves and how they become trapped in these static patterns. According to the study, one of the key conditions for the patterns to become stuck is the formation of a 'double-jet' - seen at times throughout the animation, when a second, weaker band of winds (in blues and greens) appears closer to the pole, while the main jet (greens through reds) is still flowing through the mid-latitudes (over Canada and the U.S.). You can see this double jet in the image above, and it shows up again just at the end of the animation as well.
The animation also shows the long-lived nature of some of these patterns, as one develops at about 12 seconds in, and lasts until the 19 or 20 second mark. With each second of the animation representing 1 day, that's at least a week of persistent weather conditions. This could mean a week-long heat wave for anyone living in the central part of North America (in the above image), and an equally-long period of chilly cold or extreme storms for those along the eastern part of Canada and the United States.
Lately, global warming has been implicated in the fact that we're seeing more of these extreme patterns in the jet stream, largely due to the unprecedented warming that's been seen in the Arctic in recent years. This is due to a process called Arctic Amplification, where less sea ice in the Arctic Ocean to reflect sunlight back into space means more heat being absorbed into the ocean waters. This not only melts more ice, causing something of a cascade effect, but it also means that it takes longer for the Arctic to cool down in the winter, so there's even more open ocean for longer. This causes the overall temperature difference between the equator and the pole to be smaller for longer periods of time, and we get these persistent large meanders in the jet stream. While the process of Arctic Amplification is well known, and linking it to the processes of global warming is easy enough, it's still difficult to point to these events and definitively say in each case 'That was caused by global warming.'The top video shows exactly how our increasingly erratic jet streams produced by a marked reduction in the temperature differences between the poles and the equator are creating our increasingly erratic weather patterns. As we are making dramatic changes in our atmospheric makeup by relentlessly dumping billions of tons of carbon into the air, we are destabilizing the weather patterns we've built our civilizations around for millennia.