I know it can be difficult to believe it after seeing how more than 300 liters per square meter fall in Ibiza and its streets They become Ríosbut there is life after Hurricane Gabrielle and the episode of torrential rains of recent days.
What happens is that, in the short term, that life is dry. Very dry. And the reason has a name and surname: positive nao.
What is positive nao? The North Atlantic oscillation It is the ‘dance’ between the Azores anticyclone and the loss of Iceland, the two great atmospheric phenomena that govern the meteorology of the North Atlantic.
When the index we use to “measure who is winning” is negative, the anticyclone of the Azores is weaker than normal and, therefore, cannot block the deep storms of the Atlantic. The direct consequence is that, they circulate further south than usual: just our latitude.
Now, on the other hand, the indicator is positive and that means that a drop of moisture will not enter from the west. The storms will move towards high latitudes (near Iceland and the Nordic countries).
That does not mean that it will not rain in the next few days. No, it is a bit more complex. Because it will rain (residual showers) in the Mediterranean. But as the lifting and cold air flow is blurred, the pattern change will be radical.
The start date is clear. As of Saturday, October 4, That pattern change will become a patent Throughout Western Europe: the areas of the south of continent will be under the influence of a huge area of high subtropical pressures.
What we are not so clear is when to end. On paper, the situation seems very persistent and we can almost take it that will be with us at least a week. That is between 1 and 3 degrees above normal. Not much, but notable.
However, we are in autumn and That means “A tremendously unstable atmosphere.” No one knows what will happen next.
The danger of the north. Above all, because positive nao means a blockade in the west, but It does not imply anything about the north. At any time, a Dana could be offended from high latitudes and revolutionize the tranquility of the next few days.
And it is not good news? In isolated terms, the truth is that it is neither good nor bad news. It is what there is. In the end, the country’s reservoirs They are much better Not only last year, but the average of the last ten years.
But that “water mattress” will not last forever and, although we usually forget it, autumn is an especially important station for reserves. “In general terms, autumn usually records more accumulated than winter in the whole of our country,” Yurima Celdrán said.
If we lose it, we will be facing the next drought with a hand tied behind the back.
Image | ECMWF
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