Nearly 4,000 flights were canceled across the United States on Saturday as a massive winter storm swept through the country, causing power outages and threatening severe disruption in eastern states. Forecasters warned of historic snowfall, freezing rain, and dangerously cold temperatures affecting the eastern two-thirds of the nation, with record electricity demand predicted and volatile energy prices reported in several regions. Grid operators and utilities have taken emergency measures to prevent blackouts, while airlines and local governments have declared weather emergencies and urged residents to stay safe. The National Weather Service cautioned that hazardous conditions could bring widespread closures and significant disruptions to daily life.