A rare but impressive weather phenomenon.
A rare meteorological phenomenon. Sunday afternoon, while vacationers enjoy the sun at the beach, an unexpected spectacle occurs in the sky. On the horizon, a dark and long mass as a snake appears above the ocean. In a few minutes, this monumental cloud begins to get closer to the shore, sowing fear among the bathers. “”We all believed in a tsunami“Reports a witness.
The beauty of the phenomenon is not enough to reassure witnesses. “”The most frightening was the sudden wind and this light that turned to dark gray“, says another vacationer. In a few moments, the atmosphere changes at all, pushing families to bend an emergency luggage. On social networks, the videos captured by drone show a gigantic white roller, perfectly aligned on the horizon, slowly advancing like a wave ready to surge. No one has ever seen that. This unusual spectacle immediately provokes: what is it?
This impressive meteorological phenomenon has a name: the “Roll Cloud” (or “Roll Cloud” in English). Exceptional and spectacular, he flew over the west coast of Portugal between Peniche and Povoa de Varzim, pushed by powerful gusts of wind. An area located less than two hours by plane from the southwest of France, which makes the event all the more striking for European observers. The Portuguese National Meteorological Agency (IPMA) confirmed on June 30 on its Facebook page that it was neither a montage nor a visual effect.
Looks scary, but cool
A giant tsunami cloud engulfed three cities in Portugal
This rare meteorological phenomenon, known as a “roll cloud” or arcus cloud, is a primary indicator of a powerful storm and hurricane. pic.twitter.com/7yL0FDNIxF— Military Conflicts (@Alex_RobertsJ) June 30, 2025
On the weather level, this type of training is difficult to plan. It was only officially recognized by the World Meteorological Organization in 2017, which says a lot about its rarity. The roller cloud is often born on the edge of a stormy thunderstorm or forehead. It is the mixture between hot air on the surface and downstream air (often following a thunderstorm) which causes horizontal rotation of the air, giving this roller shape.
Unlike a tornado or a funnel cloud, it does not touch the ground and is not dangerous in itself, even if it can be accompanied by boys of sudden wind. It is better to be cautious during its passage, because these winds can surprise and cause sudden movements of the air, especially by the sea.
