PHILADELPHIA — Commuters faced slippery, slush-covered roads on Friday after yet another winter storm brought snow and ice to the East Coast, leaving at least 21 people dead, including a pregnant woman struck by a mini-plow in New York City whose baby was then born by cesarean section.

The latest go-round of bad weather began overnight in some places — just in time to delay tens of thousands of deliveries of Valentine’s Day flowers — as snow, sleet and rain fell on roads already covered in many parts of the Northeast with deep puddles and icy patches.

By the time it stopped in Pennsylvania, 22.5 inches of snow was reported in Somerset County, 20 inches in Berks and York counties, and almost 19 inches in Allentown, according to the National Weather Service. Parts of upstate New York got between 12 and 27 inches of snow.

The sloppy mix of snow and face-stinging sleet grounded more than 6,500 flights nationwide on Thursday and closed schools, businesses and government centers. About 1.2 million utility customers lost power as the storm moved from the South through the Northeast, dropping to about 440,000 outages by Friday morning, mostly in South Carolina and Georgia.

“Every time it snows, it’s like, “Oh, not again,’” said Randal DeIvernois of New Cumberland, Pa., which had about 10 inches of snow by midafternoon Thursday. “I didn’t get this much snow when I lived in Colorado.”

By Friday morning, the number of flight cancellations dropped to about 1,110 nationwide. Many schools remained closed in Connecticut, Maine, Massachusetts, New Hampshire, New York state, Pennsylvania, Vermont and Virginia, while some in Rhode Island were opening late.

The treacherous weather was blamed for nearly two dozen deaths, many of them in motor vehicle accidents.

In New York, 36-year-old Min Lin died after she was struck by a utility vehicle with a snowplow attached to it as it backed up outside a shopping center in Brooklyn. She was rushed by paramedics to a medical center, where her nearly full term, 6-pound, 6-ounce baby was delivered via cesarean section, hospital spokeswoman Eileen Tynion said.

The baby was in critical condition in the neonatal intensive care unit, she said.

No immediate charges were brought against the snowplow operator.