A powerful winter storm sweeping across the United States has claimed at least 11 lives, triggered widespread power outages, forced mass flight cancellations, and prompted authorities to warn residents to stay off the roads.

The storm, which dumped heavy snow, sleet, and freezing rain from Texas to New England, has also ushered in dangerously low temperatures expected to persist through the week.

New York City Mayor Zohran Mamdani confirmed that five people were found dead outdoors over the weekend, stressing the deadly risks posed by extreme cold. “There is no more powerful reminder of the danger of extreme cold,” he said.

In Texas, authorities reported three fatalities, including a 16-year-old girl who died in a sledding accident. Louisiana’s health department confirmed two deaths linked to hypothermia, while one person was killed and two others injured in a winter weather-related road crash in southeast Iowa.

PowerOutage.com data showed that more than 820,000 customers were without electricity nationwide as of Monday, with the worst-hit areas in the southern states. Tennessee recorded over 250,000 outages after ice downed power lines, while Louisiana and Mississippi each had more than 100,000 customers in the dark.

The outages have heightened risks in the South, where severe cold is uncommon, and the National Weather Service warned that temperatures could reach record lows.

Authorities across several states urged residents to remain indoors. “Stay off the roads unless absolutely necessary,” Texas’s Emergency Management Division warned in a post on X.

The storm continued moving through the northeastern United States and into southeast Canada on Monday, with parts of Toronto experiencing record-breaking snowfall. At least 20 states, along with Washington, D.C., have declared states of emergency.

The National Weather Service warned that heavy ice accumulation could result in prolonged power outages, extensive tree damage, and extremely dangerous travel conditions, particularly in states unaccustomed to severe winter weather.

Meteorologists also cautioned that life-threatening cold could linger for up to a week after the storm, especially in the Northern Plains and Upper Midwest, where wind chills could plunge below minus 50 degrees Fahrenheit, conditions capable of causing frostbite within minutes.