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Submitted by George Elliott on Sun, 05/05/2013 - 9:01am.
Let’s face it, for much of the past couple of months, and in particular the past couple of weeks, the weather across the country has been very unusual. It’s not only the type of weather, but the persistence of the pattern that has created the anomlies.
This happens, of course, and it happens rather frequently through the year over various areas of the globe. The culprit in these kinds of persistent weather patterns is referred to as “blocking.”
Atmospheric blocking leads to the stagnation of the normal flow of air across a large area, and in fact, can affect the entire global atmospheric flow pattern. The main areas of these blocking patterns occur high in the atmosphere, usually around 18,000 feet or so, and disrupt the normal jet stream air movements. Jet streams are narrow bands of high-speed winds, and at levels in the atmosphere we are talking about, act as the guiding flow pattern to weather systems at the surface.
As you know, one things connected to the other in the atmosphere, and the resultant long-term flow pattern and surface weather patterns have been stuck, so-to-speak, and it’s been stuck in a pattern that favors very cool temperatures compared to normal over much of the eastern two thirds of the country.
Not only that, the length of time it’s been stuck, coincident with some rather strong areas of low pressure (storm systems) that have developed over the Rockies and Plains during this period (that’s part of the result of these kinds of blocks) have produced record snowstorms over the Plains and Midwest. As a matter of fact, some areas received more snow in April than they received all of last winter. Not to be outdone, May continues with the blocking pattern, and more record snowfalls occurred.
Compared to last season, 83 percent more daily snowfall records have been set so far.
Also, without getting into detail (we’ll save that for the classroom) a near-record low value of the so-called “Arctic Oscillation,” which is the climate index that measures the difference in relative pressure between the Arctic and mid-latitudes has occurred. It’s one of the strongest pressure differences measured (number 6), ranking in the top ten since records have been kept, which goes back decades.
By: George Elliott