The severe winter storm that dumped heavy snow, sleet, and freezing rain across the South and East Coast is putting strain on the largest grid region in the United States, with lingering low temperatures causing all-time highs for power demand.

PJM Interconnection, the largest grid operator and wholesale electricity market in the country, warned on Monday that more than a dozen states and the District of Columbia could experience historic strain on their electricity grids through the rest of the week.