December weather: very hard winter, like it used to be. Frost and snow in Italy
Before Christmas, one might arrive big surprise. December is now upon us and therefore curiosity is growing to know what the beginning of winter will be like. Well, thanks to seasonal forecasts, as well as some atmospheric indices, we can already get a general idea of what will await us. Polar vortex, which could reserve twists with snowfall up to the plains already before the Christmas holidays. They try to understand better what it is, in order to clarify this sensational hypothesis.
At this time of year, in the high latitudes, beyond the Arctic Circle, as usual a mighty cyclonic structure is formed which takes the name of Polar vortex. We can imagine it as a vast area of low pressure, inside which all the cold that is continually produced on the Arctic ice sheet is enclosed and which finds its outlet through the depression centers directed towards the South and therefore as far as Italy. These low pressure centers are responsible for phases of intense bad weather and drastic drops in temperatures. The behavior of the Polar vortex, however, it is not always the same.
For example, if it is strong and compact, the cold remains confined to North Pole, which is why a stable weather with high pressures and milder air is to be expected over Italy. If, on the other hand, the Vortex goes into crisis, the effects can be more or less intense. Sometimes it can literally divide into two or more parts, moving with its load icy and unstable currents towards the South. When it splits / weakens the probability that the cold also reaches our Peninsula increases considerably. This configuration was at the origin of the most intense waves of frost which invested the whole of Europe (including Italy) in 1929, 1963, 1985, 1996, 2012 just to name a few. The cause of this split in the Polar Vortex is to be found in the influx of decidedly warmer air in the upper atmosphere, in technical term stratwarming.
SURPRISES BEFORE CHRISTMAS: An influx of “hottest” air in the stratosphere (between 15 and 30 km high) with values up to + 15/20 ° C compared to the average species between North-Eastern Siberia and Alaska. It is a rather anomalous event at this time of the year and in fact it could immediately destabilize the Polar Vortex with consequences also on the European sector.
If this were confirmed, at the beginning of December masses of cold air descending from the Arctic could launch their attack towards Europe, thus causing an early arrival of cold and snow at low altitudes also on Italy. Hence, a nice snowy surprise could materialize well before Christmas, a bit like what happened last year, when the snows reached many areas of the Po Valley, whitening cities such as Turin, Milan, Padua, Venice and Bologna.
source www.ilmeteo.it
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