Beachgoers along Portugal’s coast were left in awe on Sunday, June 29, when a rare and dramatic “roll cloud” swept across the sky, resembling a giant ocean wave. The unusual cloud formation appeared suddenly during a record breaking heatwave, with temperatures soaring to nearly 116°F in central Portugal.
The horizontal, tube shaped cloud moved quickly over the Atlantic Ocean toward beaches in northern and central Portugal, including Buarcos beach in Figueira da Foz. Videos shared online show the cloud forming rapidly and stretching across the sky. “See how quickly it came?” said beachgoer Tiago Pinho, who filmed the scene. “There was a clear sky; it came in one minute.”
Known as a “roll cloud” or arcus cloud, this weather phenomenon is rare and usually forms along the leading edge of a cold front or thunderstorm. According to the U.S. National Weather Service, roll clouds can span hundreds of miles and appear detached from other storm clouds.
Climate expert Paulo Ceppi from Imperial College London explained that while these clouds look intense, they’re not dangerous. “They look scarier than they really are,” he told The Washington Post. He noted that Portugal’s extreme heat combined with cooler ocean air created ideal conditions for the cloud to form.
Climatologist Mário Marques said the cloud did not cross onto land due to the high land temperatures, causing it to appear “frozen” like a wave about to crash but never quite landing.
Scientists say that rising global temperatures are contributing to the increase in unusual weather events. Ceppi warned that such rare formations might become more common as climate change accelerates. “There are more worrying things about climate change,” he added, “but this is a sign of what’s changing.”
Although the roll cloud brought no harm, it offered a stunning and rare sight to onlookers and a visual reminder of Earth’s shifting climate patterns.
