The coldest months of the year are expected to pose an increasing challenge to the power grid, NERC said in its long-term assessment. Winter peak demand is expected to grow by 245 gigawatts over the upcoming decade. While U.S. power demand largely peaks in the summer, the growth in winter peak demand is outpacing growth in summer demand as more heating systems electrify. Power reserve margins are expected to shrink in many of the regions as rising demand outstrips new supplies, according to the assessment. In the Midwest U.S. grid, MISO, reserves are expected to fall to 4% from 11% over the same period.