A rare atmospheric phenomenon is behind the recent power outage, according to Portugal’s electricity grid operator.

REN, the operator of Portugal’s electricity network, announced that the widespread power outage affecting the country was triggered by a problem originating from the Spanish power grid. According to the company, the cause of the issue is linked to a “rare atmospheric phenomenon,” which set off a chain reaction across the interconnected European system.

As REN clarified, sharp temperature changes occurred in Spain, causing “abnormal oscillations” in high-voltage transmission lines. This phenomenon, known as an “induced atmospheric disturbance,” impacted the stability of the system and led to synchronization failures between different parts of the electricity grid.

The failure in synchronized operation triggered successive disturbances across the European power supply system, REN stated.

Due to the complexity of the technical issue, REN warns that full restoration of normal network operations could take up to a week.

“No indications of a cyberattack”

Meanwhile, European Council President António Costa stated that there are no indications the outage was caused by a cyberattack.

Costa mentioned he is in contact with Spanish Prime Minister Pedro Sánchez and Portuguese Prime Minister Luís Montenegro, and that network operators in both countries “are working to identify the cause and restore the electricity supply.”