Here are the salient questions and answers to understand how hailstones are formed, why they have different shapes, sizes and weights, if possible to predict a hailstorm and if there is a correlation with climate change. The weather until mid-August
How does hail arise?
a form of precipitation composed of ice grains, whose dimensions are greater than five millimeters. They form inside the cumulonimbus (the typical cloud of thunderstorms that rises even above 10 kilometers of altitude) in its upper part. Then, the strong hot and cold currents inside the cloud make the grains go through different motions, ascending and descending. Each time the grains make this path they swell more and more, up to a critical point that causes them to fall. The intensity is estimated with reference to the damage caused. To do this, the so-called “Torro scale” is used which goes from H0 (when there is no damage) to H10 (when houses are destroyed or seriously damaged and there are dead or injured people).
The one that hit the record-breaking Emilia on Monday?
Seeing pictures of cars with damaged windshields has impressed many but, in the past, there have been cases of grains weighing well over a kilo. For in the normal summer a hailstorm like that of Monday can arrive. Especially in the Po Valley which is among the most affected by the problem on Earth and which is often compared to Nevada, in the United States, where a similar condition occurs. instead, in particular, the increase in events in Northern Italy in recent years should be considered: from Lombardy to Trentino. It also does a lot of damage to agriculture because it destroys crops. The damage is caused by the size of the grain and the speed of fall. The hardness, shape and orientation of the fall trajectory are also considered.
What determines the size of the beans?
The size is proportional to the power of the turbulence because the stronger the winds rising from the bottom of the cloud, the heavier the grain will be. The heavier it weighs, the more rapidly and dangerously it falls towards Earth. The shapes can be different: sometimes they are spherical, ellipsoid or irregular. The cross-section of a grain tells its story and some have shown up to 25 layers of ice.
Can hailstorms be predicted?
Unfortunately, there are still no tools capable of predicting exactly where the beans will fall days in advance. More or less we can do it only with an hour or two in advance with a probability of 90 percent. This is because hailstorm is a very localized phenomenon. If it falls abundantly in North Rome, it does not reach the South.
Is there a correlation with climate change?
There are many ongoing studies on the subject and, currently, we can say that an indirect relationship. The consequences of climate change are evident throughout the planet and are also manifested by the intensification of extreme weather phenomena which are not only becoming more violent, but also more frequent.
What can man do?
If thanks to our behaviors we really reached decarbonisation by 2050, the Earth would thank us very much.
Will the weather remain erratic until mid-August?
Except for a brief respite between tomorrow and Saturday, Italy will continue to be divided in two until the 15th with high temperatures in the South and very variable weather in the North. The reason is why a wave of hot air arrives from the Sahara that goes as far as Emilia Romagna and here it collides with the cooler and humid air that comes from the Atlantic and creeps into Western Europe. This contrast creates daily thunderstorms in Triveneto, Lombardy and Piedmont. Next Sunday, in this area, strong thunderstorms could arrive while in the South there will be a heat wave with temperatures that will reach 45 degrees in Sicily and, in particular, in Syracuse, and 42 in Foggia, Taranto, Lecce.
(Marina Baldi, researcher at the Institute of Biometeorology of the National Research Council and Antonio San, meteorologist and founder of the Ilmeteo.it portal answered)
July 27, 2021 (change July 28, 2021 | 17:52)
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