New Mexico’s governor declared an emergency Thursday after a powerful winter storm left tens of thousands of people without power as heavy snow, fierce winds, and freezing temperatures marched across the northern two-thirds of the state and into Colorado.

Several feet of snow were expected to fall in parts of New Mexico and Colorado over the next three days in what meteorologists said could be the worst blizzard to hit the region in decades, as the authorities warned of dangerous road conditions and power outages.