A rare “roll cloud” stretched roughly 150 kilometres along Portugal’s Atlantic coast on Sunday, 29 June, startling beachgoers from Figueira da Foz to Vila do Conde and darkening skies over Cabo da Roca, Peniche, Ovar and other resorts. Videos showed a tube-shaped bank of cloud advancing like an ocean wave before a surge of wind sent swimmers scrambling for cover. Portugal’s Institute for Sea and Atmosphere (IPMA) confirmed the formation, classifying it as a volutus cloud—an uncommon horizontal cloud that appears to rotate around its long axis. Meteorologists said the structure formed when a mass of cool marine air undercut much warmer air lingering over the coast during the country’s ongoing heatwave, which has pushed inland temperatures to about 42 °C. Although the cloud’s arrival was accompanied by a brief, violent gust front, authorities reported no injuries or material damage. Roll clouds are better known in northern Australia’s Gulf of Carpentaria, and were only added to the World Meteorological Organization’s International Cloud Atlas in 2017, making Sunday’s sighting one of the rare documented occurrences in Europe.