What caused it? The Portuguese prime minister, Luís Montenegro, said that the issue originated in Spain. Portugal’s REN said a “rare atmospheric phenomenon” had caused a severe imbalance in temperatures that led to the widespread shutdowns.

REN said: “Due to extreme temperature variations in the interior of Spain, there were anomalous oscillations in the very high voltage lines (400 kV), a phenomenon known as ‘induced atmospheric vibration’. These oscillations caused synchronisation failures between the electrical systems, leading to successive disturbances across the interconnected European network.”

https://www.theguardian.com/business/2025/apr/28/spain-and-p...