By Alice Sjoberg
A severe heatwave recently swept across Southern Europe, with temperatures in Spain, Portugal , Greece , and France soaring above 40C. This prompted countries to promptly issues warnings of extreme heat, wildfires, and health concerns as they urged people to stay away from the sunshine and keep themselves safe. However, beachgoers in northern Portugal were caught off guard when a rare ‘ tsunami roll’ suddenly appeared in the sky over the water, prompting them to quickly scramble for shelter. This unusual weather phenomenon consisting of a dark wave of clouds was yet another consequence of the extreme temperatures that had been gripping the country. The cloud resembled a massive wave crashing through the sky, with beachgoers gazing upwards in awe as the sky suddenly darkened and turned ominous. The tsunami-like cloud had quickly engulfed the previously clear blue sky. A social media user took to Twitter to share photos and videos of the spectacle, showcasing the cloud rolling horizontally across the sky, mimicking the curl of an ocean wave. They wrote on the post: “It was nuts to have experienced this rolling cloud in the north of Portugal. Felt like a tsunami out of a movie!” “Apparently it was 150km long, stretching from Figueira da Foz all the way up to Vila do Conde, which is close to where I was,” they added. Although the tubular, wave-like clouds sparked panic among some beachgoers, who feared it was a sign of an impending tsunami, the breathtaking sight was actually a natural phenomenon known as an arcus cloud, or roll cloud. The phenomenon is more frequently spotted in the southern hemisphere, particularly down under in Australia . It emerges when frigid airstreams collide with scorching temperatures. Characterised by a horizontal tube formation that hugs low in the sky, creating an arcus cloud, roll clouds are “relatively rare,” the National Weather Service (NWS) reports. “Roll clouds usually appear to be ‘rolling’ about a horizontal axis, but should not be confused with funnel clouds,” the NWS explained. These sinister-looking clouds are birthed from thunderstorm fronts, which dispel cooler air, leading warm, damp air to coalesce into a cloud that may become ‘entrapped’, commencing its rotation on a horizontal plane. After Portugal’s coasts sweltered over 40C, the conditions were ripe for witnessing this spectacle, soon followed by lashings of rain, thunderclaps, and even hail stones post-roll cloud spectacle. Cue the rush to Twitter’s comments section, where netizens expressed their awe for the meteorological marvel. “NGL but I’ve never seen anything like it,” one viewer said, as another said: “Unusual and impressive.” “That’s pretty wild! So fast, too,” commented a third user. An excited fourth viewer said: “It started in Peniche! So, it was even bigger!”. Reportedly extending over 90 miles along the Portuguese coast, the roll cloud caught eyes from Vila do Conde to Figueira da Foz, as reported by locale news sources.