Millions of people across the Midwest, Northeastern United States and southern Ontario, Canada, were under winter weather warnings Thursday morning as snow squalls moved through ahead of another blast of Arctic temperatures.

After a week of bitterly cold temperatures and days of lake-effect snow, another shot of cold air was sweeping through the Northeast after sending temperatures in parts of the Midwest plunging into the teens, 10 to 20 degrees below normal. Wind gusts up to 50 miles per hour are expected Thursday, bringing blizzard conditions to areas with lake-effect snow and making travel treacherous.

Forecasters with the National Weather Service in New York City said that Thursday night into Friday would be the coldest night and early morning of the season, especially after accounting for wind chill.

In New York, which experienced one of its warmest Halloweens ever this fall, some welcomed the return of more-seasonable temperatures. At an outdoor Christmas tree lot in Midtown Manhattan on Wednesday, Rosie Roop, 25, a hospitality and business student, was buying a wreath. “I’m happy it’s getting colder,” she said. “I just want it to snow.”

Ms. Roop said she had worn her puffy coat for the first time this week. “I definitely like the four seasons,” she said. “I have not been a fan of the murky in-between.”

The chilly weather inspired Danny Offermann, 28, an assistant principal at a charter school in the South Bronx, to visit a Christmas tree lot and buy a two-foot tree ($60) for his apartment.