Jim Andrews

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What Is a Greenland Block?

February 21, 2006; 8:04 PM ET

February 21st

One of my earliest postings dealt with `blocking highs`, which I tied in with cold waves over Europe. Wherever they form over polar belts in the cold months, blocking highs are wont to make for anomolous patterns of temperature, be it above or below what is `normal` for the area in question.

A blocking high is marked by relatively high pressure through a deep layer of the atmosphere. In the Northern Hemisphere, steering winds tend to wheel about such a high in a clockwise sense about a broad core having weak wind flow. Such highs can spread for 2000 or more miles (3000 or more km) in all directions. Where such a high is found instead of the usual westerlies aloft (the jet stream), the west-to-east progression of lows (wave cyclones) and cold fronts is disrupted. Indeed, it may be shunted far to the north by the block, which would likely pump warm air towards the Pole; or shifted southwards, which can lead to stronger, wetter lows/fronts than accustomed in the mid latitudes.

Such a blocking high will likely set up shop over the northern Atlantic basin including Greenland and Iceland at the latter half of this week. The western limb of the high will drive anomolous warmth northwards and westwards over Greenland to the Baffin Bay. At week`s end, even Baffin Island itself will likely warm anomolously.

Now, when a blocking high is parked east of northern North America, the usual dumping ground for arctic air offloading the continent, whatever arctic air is present must go somewhere else. Invariably, that `somewhere else` is to follow a more southerly path that takes in eastern Canada and at least some of the United States. Well, this is precisely what is being forecast by a consensus of computer models for the end of this week and the first half (at least) of the next. Canada`s `storehouse of cold` is not fully stocked right now (northern Quebec and most of Nunavut have the truly cold stuff). However, the Arctic Ocean basin off northwestern North America and northeastern Asia is shown to grow steadily colder for the next few days with northwesterly wind flow set to pour some of this arctic cold into the heart of Canada. From here, it will be free to take the `straight shot` over the line to the eastern two-thirds of the United States.
From here, the cold will take the path of least resistence in an attempt to re-join the west-to-east trend of the jet stream: out to sea from the Eastern Seaboard.

Want to gain more insights as to the impact of the upcoming United States cold wave? Check out our other columnists, for some of them will be weighing in on this big weather story right into the coming week.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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