Unprecedented electricity demand and lagging infrastructure development could place many regions of the U.S. at risk of power supply shortages over the next decade, particularly during periods of extreme weather, the North American Electric Reliability Corp. says in a new report. Over the next five years, NERC forecasts that all or parts of 19 states from Montana to Louisiana are at high risk of rolling blackouts during normal peak conditions. And most of the rest of the country is at similar risk when demand for electricity spikes during exceedingly hot or cold temperatures.