It is meteorological winter: in the field of weather, by international convention it starts three weeks before the astronomical one. And in everything the Northern Hemisphere (boreal) we are observing typical winter weather conditions. Well, last year in some areas of Italy it had been even worse, for example the first snow in the Po Valley had arrived these days, but this year, again in a limited area such as the Italian one, snow has come abundantly on the reliefs of the Peninsula up to medium-low altitudes, even very low as is the case in Sardinia (even at 300 meters north of Cagliari).
The cause we have given to this event are La Niña and the Polar Vortex which has loops that trigger cold waves in various areas of our hemisphere, with unusual snowfalls, in quantity, such as in Japan, Mongolia, China.
La Niña loses strength, Polar Vortex can be attacked. The danger of unexpected Frost Waves germinates, what does all this mean?
In short, La Niña is an ideal condition for phases of bad weather in the Mediterranean. A circulation of the Weak polar vortex favors the genesis of loops; therefore, it affects the Jet Current flowing more undulating than usual, favoring cold waves and bad weather. In this context, there is also the expectation of an eventual Strat Warming, one has already occurred early in the Siberian area a month ago, but those riskier for us are unleashed in the polar region.
No one is able to predict them well in advance.
The effect of a Strat Warming on the Polar Vortex is often its split (but not only) or the genesis of two vortices and the possibility of a change of atmospheric circulation on the ground, which reverses taking a direction from east to west, pushing the Siberian cold to Europe. This would mean waves of frost. Well, the point of this article is that there is a greater chance than in other years for this to happen.
Eg, a stratospheric warming event that occurred in mid-January 2012 contributed, both to reinforce the Russian-Siberian anticyclone, and to a large-scale change of atmospheric circulation, which it inundated Italy and Europe with frost. Similar synoptic configurations also occurred in the well-known cold waves of 1956 and 1985.
Modern science can trace ideal conditions for possible scenarios, but it has no certainties, being complex weather events. Phenomena that a period such as that between 1600 and 1800 were frequent, lasting and impressive. The last of these so serious took place between January and February 1929, They are followed by those of 1956 and then 1985 for their grandeur, importance and duration.
But let’s get back to The girl which in the Southern (Southern) Hemisphere is causing heat waves and extreme weather, with intense thunderstorms that add to the effects of climate change.
Last summer many Mediterranean countries did not look like postcards. There was talk of tropicalizzazione of the climate, from asphyxiating heat and records of high temperatures, drought, fires, and then mixed with all this, sudden days with thunderstorms. But the most widespread phenomenon is the large hail that fell in many regions was serious.
Hail that has affected Italy especially in Northern Italy devastating countryside, where it destroyed crops, damaging flora and killing the most exposed fauna such as birds. Some hailstorms are known because they occurred in the vicinity of large urban centers, if not metropolises, others because they devastated thousands of cars on the motorway, whose images have traveled around the world. Then fires, the worst occurred in Greece and Turkey, where for days and days the sky from the Hellenic Peninsula to the Aegean was clouded by smoke.
An extremization of the climate is underway which has causes due to human activities, which is added to natural ones: climate fluctuations.
But hail has been seen in other parts of the planet, in areas where these weather events never happened, such as coastal Australian cities. And anyway, the list is too long to report here.
And last summer there was also extreme heat. The strangeness of autumn is that in this new season (winter) the super floods are handed down to us in some areas, such as those of the American region of Vancouver, the same regions of record heat, where last summer almost 50 ° C was reached. .
The violent summer weather conditions, the adverse winter ones with record cold waves, were feed the girl. The November 30 also the World Meteorological Organization issued a statement on the matter. According to forecasts, La Niña will be weaker, but it will last until the end of this winter in the northern hemisphere (ours), perhaps prolonging its presence until early spring 2022.
La Niña in Spanish means young girl or child. La Niña is, to put it briefly, the opposite of El Niño, another climate behavior pattern said is part of teleconnections. Together they form one of the most meteorological phenomena important in the world.
The El Niño-Southern Oscillation (ENSO) flows back and forth across the Pacific Ocean every few years, changing the temperature of the surface waters, consequently affecting the atmosphere.
La Niña, when it is strong, generates devastating weather events in large areas of Pacific countries, but it is done feel up to Europe, where it combines with other climatic patterns of behavior. But as it loses power as it is starting to happen, other patterns come into play, and for example, the role of the Polar Vortex which in Europe and Italy can favor sea Arctic cold waves, how it is going to happen again, and how it should happen in the next few weeks as well.
Invasions of the polar vortex towards the south generate cold which is established in the Po Valley, which traps it due to its geographical conformity. Low solar radiation attenuates the sun’s heating; moreover, the advent of foggy periods or bad weather results in those ideal conditions for snow in the plains, generating the famous Padano cold air cushion. This is sometimes persistent and very intense.
And this condition occurs in cycles, certainly mitigated by the warming of the climate, by the strong urbanization that generates immense islands of heat. A cycle of heavy snowfalls in the Po Valley it took place in the 60s and mid-80s of the last century, and then in the first decade of this millennium. One of the major events was that of the end of January 2006.
But the frost wave of February 2012 was notable, when for two weeks the whole of Italy was affected by cold and snow, but to generate it it was a change in the circulation of the Polar Vortex, which due to the Strat Warming it reversed, pushing air masses from Siberia to the heart of the Mediterranean. Minor events happened later, even if the one in 2018 (late February, early March, was very violent).
What to expect, a seasonal continuation with La Niña losing strength, a vulnerable Polar Vortex which this year has more possibilities to split in two following a stratospheric warming: Strat Warming.
To be clear, there are various ingredients to churn out extreme winter weather events.