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High latitude ridge could bring below normal temperatures

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.

Medium range forecast models have been consistent in developing a mid level ridge from the Northwest Atlantic Ocean into Greenland, with higher than normal heights extending toward the Davis Straight in Canada. Although this ridge isn’t closed off or a dominant, pattern-controlling blocking ridge of its own, it’s enough to slow down the pattern around it and displace a mid and upper level trough from Central Canada into the Northeast United States next week. And so, not surprisingly, cooler than normal air is expected in our area.

GFS model forecast height anomalies for 120 hours at 500mb. Notice above normal heights in the NW Atlantic and Greenland (ridge) and the resulting cooler than normal heights in our area.

GFS model forecast height anomalies for 120 hours at 500mb. Notice above normal heights in the NW Atlantic and Greenland (ridge) and the resulting cooler than normal heights in our area.

The longevity of this pattern can be put into question, as teleconnectors don’t necessarily favor a prolonged blocking episode. Still, models are consistent in not only developing a ridge from the Northwest Atlantic into Greenland and the Davis Straight, but also a ridge on the West Coast of the United States. This is likely to aid in the transport of cooler than normal temperatures into our area by next week — and a large upper level trough into Southeastern Canada.

What does this mean for us? Well, in terms of sensible weather it means that a cold front is likely to move through our area later this weekend with showers and possibly a thunderstorm. Behind it, blustery northwest winds are likely to usher in some very cool-feeling Autumn air. And by the time next week rolls around, an airmass source from Canada is likely to keep the warmth away and, in fact, keep below normal temperatures (noticeably so) in our area for several days before the airmass modifies.

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