In recent weeks we have repeatedly talked about the importance of two descriptive indices of particular hemispheric baric conditions: the AO index and the NAO index.
We want the article to be aimed at everyone, not just those who are familiar with the subject and with the analysis of certain patterns. So we will try to get to the point, that is we will try to grasp the climatic weather trend of early December (beginning of the meteorological winter).
No more chatter: the AO index will return neutral or even negative. Let us remember that the index describes the state of health of the Polar Vortex: when it is positive it describes a Vortex in excellent health, when it is negative it means that the Vortex is losing its bite. Beware, it doesn’t mean he’s running into who knows what big problems, it just means he’s taking a break. Know, if it is still not clear, that we are in the presence – for a change – of a super Polar Vortex. And if it results in yet another silly winter, well, we’ll figure it out as we go.
The fact is that a loosening of the Vortex could trigger winter dynamics on us too, perhaps through pronounced oscillations of the polar jet and consequent arctic irruptions at mid-latitudes.. This is what we have been saying for some time, namely that the first decade of December could represent the right moment for a relevant or at least interesting winter episode.
As for the NAO index, which describes the difference in pressure between the North Atlantic and the Azores, it seems to be struggling to move away from the positive territory but cards in hand could head towards neutrality (again in early December). This is good news, because in this way it would allow the High Pressure to push north and confirm the dynamics of meridian exchanges that we have just highlighted.
In short, everything suggests that we could witness a period of lower than normal temperatures, with unstable weather and with precipitation that could become snowy at interesting altitudes.
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