On June 30, 2025, a rare meteorological event known as a roll cloud appeared over parts of Portugal, surprising residents and beachgoers alike. This unusual cloud formation, which stretches horizontally and resembles a giant wave rolling across the sky, caused momentary panic as many mistook it for a natural disaster like a tsunami.

The Roll Cloud’s Appearance in Portugal

This particular roll cloud extended over three coastal cities in western and central Portugal. As it approached the beaches, sudden strong winds accompanied the cloud, surprising visitors and prompting many to leave the shore out of caution. Social media quickly filled with photos and videos capturing the eerie spectacle, highlighting the cloud’s unusual shape and size.

Why Is the Roll Cloud Important?

A roll cloud is a distinctive, horizontal cloud formation created when a sea breeze meets warmer air masses. It appears as a tubular, rolling structure moving parallel to the ground, giving the illusion of a massive wave in the sky. Despite its dramatic appearance, the roll cloud is harmless and not linked to extreme weather such as storms or heavy rainfall.

Roll clouds are very rare in Europe. The most famous roll cloud phenomenon is Australia’s “Morning Glory,” which can reach up to 1,000 kilometers in length and appears only a few times each year. Portugal’s recent sighting is an uncommon event that attracted attention for its striking visual impact.

Rising Temperatures and Climate Concerns

At the same time as this atmospheric event, Portugal is facing a heatwave, with temperatures rising steadily throughout the week. This has increased fears about forest fires, especially in the northern and central inland areas. The country’s National Authority for Civil Protection issued warnings and preventive advice to residents to reduce fire risks.

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Tourists walk in Cais das Colunas as temperatures rise in Lisbon, Portugal, June 30, 2025. REUTERS/Pedro Nunes

While the heatwave poses a significant threat, authorities did not issue any warnings related to the roll cloud, emphasizing that the cloud itself is not dangerous.

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Tourists drink soda as temperatures rise in Lisbon, Portugal, June 30, 2025. REUTERS/Pedro Nunes