Lingering US Heat Tests Grids With Power Emergency in Southeast

Dangerous heat and humidity will stress power grids along the US East Coast Friday, putting pressure on prices as the risk of severe thunderstorms spreads from the Midwest.

Temperatures are expected to spike above 100F (38C) from southern Virginia to North Carolina Friday, with sweltering humidity that makes the heat feel more intense. With cooling demand surging into the weekend, the Trump administration declared a power emergency in the southeastern US this week to shore up the grid.

An emergency order issued by the Energy Department on Thursday allows Duke Energy Corp. to operate power plants at their maximum output ...