Weather, record frost and snow. Second part of winter as it hasn’t happened for a long time
The official trend has arrived, it will be a second part of the winter out of the ordinary as it hasn’t been seen for years, even crazy. The update confirms the presence of two signs that suggest that one is waiting for us winter season of other times, characterized by a dynamic and rich climate snow up to low altitude. There are important news for January and February: we tell you the reason for this statement.
In order to understand what the next weeks and months will be like in Italy, we need to broaden our gaze to the entire hemisphere in order to highlight the players who will influence the weather. Well, compared to the last few years something anomalous in the field of atmospheric pressure is happening in the middle of the Atlantic Ocean.
In particular the climate index NAO (North Atlantic Oscillation) highlights the variation in sea level pressure between Iceland and the Azores. This pressure difference is extremely important for understanding the atmospheric conditions in the Atlantic and its meteorological effects on Europe and therefore on Italy. When the index NAO it is positive (NAO +), zonal winds from the west prevail and consequently they bring moist air from the ocean to the continent (lots of rains and mild climate).
The news just arrived is that the index after a very long time has turned heavily in negative (NAO-) and now he seems crazy: the westerly winds are weaker and the atmospheric conditions on a synoptic scale favor anti-zonal currents (from east to west), with the possibility of cold eruptions from the east.
In essence, this is a radical change: this will favor the formation of a robust high pressure field on the North Atlantic in the coming weeks. In this configuration, the anti-zonal flow will be favored and we will see incursions of freezing air descending directly from the Arctic.
Attention, the crazy surprises did not end there. To increase the risk of waves of frost the Polar Vortex destabilized by a sudden stratwarming will also take care of it: with this term, in meteorology, we refer to an anomalous and intense warming of the terrestrial stratosphere, right above the Arctic region, in the order of 20/30 ° C in the a few days.
Once activated, this heating gradually tends to expand towards the upper troposphere, with repercussions on the Polar vortex (large area of low pressure in which all the cold that continuously forms at the North Pole is enclosed): the immediately lower sector, in fact, is forced to deform (dislocation of the polar vortex) or even to divide into 2-3 distinct minima (in this case we speak of the split of the polar vortex), which then travel in part towards the mid-latitudes, causing cold waves to the heart of the Old Continent and up to our country.
To remember, for example, the historic cold wave of 1985, as well as those of 1929, 1956 and 1963, linked to a stratospheric warming of this kind.
Hence, a deadly pairing could be triggered for the fate of the second part of winter, on the one hand the NAO negative and on the other a polar vortex literally shattered.
As a result, in the coming months the interaction between the freezing cold from the east and the possible arrival of downward depressions from Northern Europe could give rise to a rather unstable period. Given the temporal distance, still too high, of course, we cannot go into details, but having said that we can still say that a very dynamic and cold phase awaits us, with the risk of snowfall up to the plains and on the coasts in the event of the formation of minimal depressions on the Mediterranean Sea.
source www.ilmeteo.it
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