Why the US and much of Europe are shivering in the cold

Why the US and much of Europe are shivering in the cold

"The folks who run the National Center for Atmospheric Research have a great rundown of the details of the AO Oscillation. In short, high pressure in the Arctic forces the jet stream south, and it drags cold air with it, chilling North American and northern Eurasia. In its opposite mode, those same regions tend to be much warmer. Right now, we're in such an extreme high-pressure event that the readings have run off the scale of NOAA's AO index. Fortunately for those hoping to warm up a bit, the AO is a weather event—it often changes states multiple times within a single season, and there's no clear evidence linking its behavior to climate trends.

The NCAR site also points out one of the reasons why people are making a big deal out of this one: we tend to think short-term when it comes to our surroundings. We haven't had an AO event this severe since 2003, and the high pressure mode has been relatively rare since 1990, so many places have simply gotten used to not having an Arctic blast during the winter. The fact that November was unusually warm in the US, Canada, and Europe probably doesn't help matters, either."