In Italy, where extreme weather events are common, it is necessary to clarify the violent phenomena linked to storms that are often confused. After violent downpours and storms that cause damage and displaced people, the word “whirlwind” is often on everyone’s lips. But often it is not a question of tornadoes or whirlwinds (the two terms are synonymous) but of downbursts.
In the video the downburst that hit the Tigullio on August 18, 2022
If as soon as violent gusts break out, people immediately cry “whirlwind” but this is almost always not the case. A whirlwind presupposes the presence of a funnel or a vortex. Very often, however, these are gusts that are also very violent, but linear, in which there is no vortex that touches the ground.
Tornadoes or whirlwinds
The tornado is linked to a storm cell where a vortex motion is triggered that originates its funnel shape. It can take on various shapes: from a very narrow funnel to a diameter of up to 2 kilometers. Furthermore, based on the strength of the wind, they are classified on a scale (Fujita) that goes from 0 to 5 with gusts of up to 300 kilometers per hour. Tornadoes are linked to a structure linked to a storm supercell that originates a Mesocyclone, a rotating storm.
When they develop in the sea or on a lake then they are called waterspouts: usually they are very thin and generally harmless vortices but when the energies in play are very strong as in this late summer they can become very dangerous for boats.
The downhill
The dynamics that trigger tornadoes are not as frequent as the damage caused by downbursts, descending winds that originate from a thunderstorm. A thunderstorm cell has warm winds that are sucked up by the pressure difference and rise inside it, and cold winds that are expelled outwards and that, when they touch the ground, fan out along the front of the storm, even exceeding 150-270 kilometres per hour.
Depending on the shape of the storm cell, it can cause damage on a wide front even over 4 kilometers. Therefore much more extensive than what happens in the cone of a tornado.
If as you can see in the images of Piombino the gusts of wind may seem extreme, the flow of air originating from storms can be dangerous when the necessary precautions are not taken. The invitation is always to pay attention to the weather alerts issued by the civil protection.
If we see a curved shelf cloud or shreds of low clouds advancing very quickly, we should expect strong gusts. Unfortunately, sometimes these signals are not perceptible; we are talking about violent descending flows that are not identifiable to the naked eye, unlike tornadoes, which are often clearly visible and documented. Therefore, the downburst is a much more insidious convective phenomenon, as the speed of evolution and its intensity are comparable to those of a medium-low range tornado, but the affected area is usually much larger and is almost always hidden by precipitation. Knowledge of this type of storm phenomenon, which has always existed and is likely increasingly accentuated by global warming, is the real weapon for our self-protection.