Hundreds of thousands of customers in the Pittsburgh area were left without power after powerful storms ripped through downtown Pittsburgh and the greater Western Pennsylvania region late Tuesday afternoon,

Electricity was back in most of the two countries after a blackout that shut down much of daily life. The cause of the outage remained unclear.

Red Eléctrica, Spain’s electricity grid operator, ruled out a cyberattack, human error or unusual weather. Experts say it could take weeks to determine the cause.