Rivers in flood, rainfall reaching up to 170 millimetres, hail with a circumference of 8 cm. Piedmont still hit by strong bad weather which struck especially in the valleys, from the Turin area to the Vco. «We found ourselves on the border between a low pressure rising from Spain towards France and a high pressure which was instead positioned over the Mediterranean – he explains Andrea Vuolophysicist and meteorologist from Weather in Piedmont –. In the Alps there was a convergence between a wind of Libeccio and Scirocco. It must be considered that two different phenomena occurred in Piedmont: Supercell storms, responsible for the heavy hail, and self-healing storms in the Alps.”
Has the humid heat of these last few days been decisive?
«Yes, it created an accumulation of heat in the atmosphere which, with the passage of this disturbance over the Alps, allowed the genesis of storm clouds. The problem was mostly represented by the stationarity of the phenomena in the mountains.”
We saw impressive images of rivers in flood…
«What happened in Bardonecchia last year happened. With these accumulations of rain, the streams undergo sudden swelling, also caused by the large quantity of snow that is still present at high altitudes, especially above 2500 metres. Yesterday it rained up to almost 4000 meters. The precipitation caused the snowpack to melt which then flowed into the streams.”
Phenomena that will occur again?
“Other strong thunderstorms are likely in the coming weeks, especially in the mountains and on the upper Po Valley. Currently the soils are no longer able to drain the falling water. It has rained too much in recent months and therefore some hydrogeological phenomena are to be expected: landslides, mudslides, debris flows, mudslides”.
Which territories could be most affected?
“In particular the Alpine sectors, from Turin to Verbano, which are the areas most affected in recent months. We consider the fact that in the coming weeks there will still be a lot of snow melting at high altitudes: therefore maximum monitoring will be necessary”.
The hail reached 8 cm in diameter. How is this possible?
«It is the consequence of the Supercella storms, which increased by almost 50% in Piedmont. Bad weather of this type has always existed in the Po Valley because it has a geographical conformation very similar to that of the plains of the great American plains, where tornadoes form. Since the Alps are also nearby, the Supercells are weaker than the American ones. But the phenomenon has certainly increased, almost doubled.”
Is the cause of these increasingly common and extreme events due to climate change?
“Absolutely. The statistics show a significant increase in events in the last decade, confirming that climate change is influencing the phenomenology.”
You talked about tornadoes, can we imagine that they will occur more and more often in Piedmont too?
«On average around thirty occur every year between Veneto and Emilia-Romagna, particularly partly also in lower Lombardy. It should be taken into account that these phenomena, by virtue of climate change, will increasingly increase in frequency and intensity. In Piedmont the areas most prone to vortex phenomena are those of the Vercelli area, Valsesia, and partly also Monferrato and Alessandria. Which are the areas that are known to experience tornadoes. Yesterday in Busano, however, was not a tornado but a Downburst, with a wind regime that is opposite to that of the tornado.”
How will July go? What are the forecasts?
“The month of July will pass with precipitation still above average and temperatures without particular excesses. So in any case we are talking about instability. In August we imagine a more stable period with the arrival of the anticyclone and therefore a warmer and longer-lasting phase. In the Alps, however, a very dynamic summer is expected”.
