(Adds crashes in Pennsylvania, snow totals, quotes, new storm on the way)
By Barbara Goldberg
NEW YORK, Feb 14 (Reuters) - The U.S. East Coast dug out on Friday from the final wallop of a deadly four-day storm that dumped more than two feet of snow in some places and made a mess of the morning commute, triggering crashes of up to 100 vehicles in Pennsylvania.
Blue skies belied a previous night of unusual thundersnow and lightning in New Jersey, and snowfall that measured 26 inches (66 cm) in Glyndon, Maryland, 20 miles (32 km) northwest of Baltimore, according to Chris Vaccaro, spokesman for the National Weather Service.
A new storm system was on its way Friday from the central Plains and expected to dump up to 3 inches (7 cm) on the East Coast into Saturday of Presidents Day holiday weekend, he said.
Ambulances rushed to treat people in dozens of flipped-over cars, jack-knifed tractor-trailers and vehicles that skidded off the Pennsylvania Turnpike during the morning commute, shutting down the major thoroughfare, according to television images.
"It was a chain reaction," said Renee Colborn, a spokeswoman for the Pennsylvania Turnpike Commission.
Colborn said authorities do not have a count of the number of vehicles involved, but television traffic reporters in helicopters described a scene involving from 50 to 100 cars.
"There must have been some type of quick freeze this morning. The sun was out. We don't have an exact reason why this accident occurred," Colborn said.
Heavy snow fell in and around New York City, Boston and Philadelphia, where schools were closed for a second unplanned day on Friday.
The winter storm system, which earlier froze the southeast in its tracks, pushed north up through the mid-Atlantic states on Thursday, with fierce winds and heavy snow causing thousands of flight cancellations and school closures from Washington to Connecticut.
The storm has also been blamed for at least 15 deaths in the South. In New York, doctors were working to save the baby of a pregnant 36-year-old woman killed by a private snowplow in a parking lot in Brooklyn. In Washington, D.C., a man was found dead on a snow-covered sidewalk, though police were unsure if the incident was weather-related.
City officials, who had grappled with icy roads and widespread power outages in Georgia and South Carolina as the storm moved up the coast, were planning accordingly.
Federal agencies in the Washington, D.C. area opened two hours later than normal and said employees had the option to work from home.
Repeated winter storms are taking a toll on schools and families, as snow-related cancellations left parents scrambling to find child-care and administrators looking at making up lost days by extending classes into the summer.
About 1,200 U.S flights were canceled and roughly 1,300 more were delayed early on Friday morning, said flight-tracking website FlightAware.com.
The weather also slowed business for flower shops banking on a big day of deliveries on Friday for Valentine's Day.
Stefan Handl, a co-owner of the Harlem Flo flower shop in Manhattan, said the huge storm "isn't making our life easier, that's for sure."
(1 inch = 2.54 cm) (Additional reporting by Karen Brooks in Austin, Texas; Editing by James Dalgleish)