'Rare atmospheric phenomenon' behind huge power outages in Spain and Portugal Portugal's grid operator has revealed a "rare atmospheric phenomenon" contributed to the power cuts – but what does this mean? Spain and Portugal has been bit by a huge power outage (Image: AP ) Chaos has erupted across Spain and Portugal as major blackouts have left millions without electricity. Madrid, Barcelona, Valencia, Seville and Lisbon are among the major cities to be hit by the power outage at around 12.30pm local time in Spain – and 11.30am in Portugal – on Monday (April 28). ‌ A graph on Spain’s electricity network website showed demand across the country indicated a steep drop at around 12.15pm from 27,500MW to nearly 15,000MW, according to PA. ‌ The outage has affected airports, traffic lights and trains across Spain and Portugal, prompting travel chaos, with the Foreign Office warning travellers that there may be "disruption". Rede Eletrica Nacional (REN), Portugal's grid operator, has since put out a statement, claiming that the outage is related to a "rare atmospheric phenomenon". It 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'". Article continues below It added: "These oscillations caused synchronisation failures between the electrical systems, leading to successive disturbances across the interconnected European network." This suggests that temperatures changed quickly in Spain, which affected the high-voltage power lines. As a result, this caused strange movements in the electricity, which made the power systems stop working together properly. Since many European countries share power systems, the problem spread to other areas, including Portugal. ‌ According to REN, it could take up to a week for the network to fully normalise again due to the complexity of the problem. Spain is yet to respond to these claims. It comes as Spain enjoyed temperatures 'well above the seasonal average' in recent days, according to Spanish News Today. The publication reports that an Azores anticyclone had led to calm and dry conditions across the country. Article continues below In recent days temperatures have hit 30c in Sevilla and 25c in Madrid.