The nation's power grid faces a sharp risk of buckling in the event of major storms or prolonged cold snaps this coming winter, according to the regulator that monitors the electricity system, with much of the country threatened with outages triggered by severe weather.

A sweeping portion of the country that extends from Texas to the Canadian border is not adequately equipped for tough winter conditions, the North American Electric Reliability Corporation warned in a forecast released Wednesday. The report is a sobering assessment of a power grid that continues to fray and suffer from underinvestment, despite promises by politicians and regulators to shore it up following deadly blackouts in recent years.