“It looked like a tsunami”: how the gigantic (and rare) rolling cloud appears on the beaches of Portugal is formed

On 29 June the North-Atlantic coast of Portugal It was the scene of an atmospheric event as rare as it is fascinating: a roll cloud or Rotal cloud, over 150 kilometers longappeared on the horizon between Figueira da Foz and Exposeleaving the swimmers who were on the beach breathless. Some described the scene like that of one tsunamifor the dramatic visual effect and the speed with which the cloud advanced.

This particular cloudy training belongs to the category of Arco cloudsand is scientifically classified as Stratocumulus volutus. Its elongated and cylindrical shape gives the impression that it is rolling on itselfpushed by the horizontal winds. , but it is certainly rare and spectacular, especially in Europe. In Portugal a similar event had been recorded very twenty years ago, near Port.

How the Roll Cloud is formed

The formation of a roll cloud It requires very specific weather conditions. At the base of the phenomenon there is a strong thermal contrast between cold and hot air. In the Portuguese case, theAtlantic Ocean recorded temperatures around the 17-18 ° Cwhile the air on the mainland had passed the 40 ° C. This marked difference triggered a flow of sea ​​breeze Which, clashing with a mass of hot and stable air, favored the onset of the typical rotation effect.

Another fundamental element is theabsence of strong windswhich allows the cloud to maintain its shape without disintegrating. When these factors align, the cloud moves in an orderly way along the coast, creating a remarkable visual impact, but without causing damage.

The roll cloud they are more common in other areas of the world, as in the Queensland Australian, where the famous phenomenon of the Morning Glory Cloudswhich can also reach i 1,000 km long. Also in Californiain Scotlandalong the Sleeve and in Alaska Similar structures have been observed, always linked to extreme but stable atmospheric conditions.