High latitude ridging has become a bit of a staple in meteorological terminology over the past several years. Much of this can be attributed to the fact that we’ve seen several record breaking episodes of it. Conversely, we’ve also seen periods which have lacked that blocking, leading to major forecast changes and dramatic pattern evolutions. High latitude blocking, or ridging, occurs when higher than normal heights build into the higher latitudes (here’s a not-so-fancy image of where the high latitudes are defined). This can occur at any time of year, but we’ve seen it in the Autumn and Winter more often over the past several seasons. High latitude ridging and blocking events can be of varying degrees, as well. Some of the less extreme examples, like this upcoming one, can produce mild pattern changes. Other more extreme examples, like the high latitude block that occurred prior to Hurricane Sandy and the Boxing Day Blizzard, can…well, you know.
Nevertheless, without getting overly technical, these high latitude blocks and ridges can “buckle” and slow down the mid and upper level atmospheric pattern. And while much also depends on what’s going on around these blocks, more often than not if they occur on the Atlantic side (Northwest Atlantic Ocean into Greenland), they result in cooler than normal air being displaced to the south of the ridge over Canada. This often leads to cooler than normal air in our region, and this upcoming event likely won’t be an exception to that rule.