UPDATE 1-Winter 'four'easter' storm hits U.S. East, snarling traffic, closing schools

schools@ (Recasts with storm hitting East Coast, adds byline)

March 21 (Reuters) - Millions of commuters along the U.S. East Coast faced another round of heavy snow, ice and gusty winds on Wednesday as the fourth major snowstorm this month struck the region, closing schools, grounding flights and halting buses and trains.

The nor'easter storm was on track to dump between 12 inches and 18 inches (30 cm and 46 cm) of snow on areas from Philadelphia to New York City on Wednesday, said Weather Prediction Center meteorologist Dan Petersen. Other cities, including Boston and the Washington area, were getting lighter snowfall.

The storm had already brought 3 inches to 4 inches (8 cm to 10 cm) of snow to Manhattan and lashed parts of the East Coast with winds of more than 50 miles (80 km) per hour, according to the Weather Prediction Center.

Airlines scrapped more than 3,890 flights into and out of the United States, according to flight tracking website FlightAware, and nearly 1,000 other flights were delayed.

Jeremy McLellan, a standup comedian from Charleston, South Carolina, posted on Twitter that his flight was canceled and that he was stuck in New York City and would miss his wife's baby shower.

"(Snow: If you can read this ... thank you.)," McLellan wrote.

The storm forced schools across the region, including those in Philadelphia and New York, the largest school district in the United States, to cancel classes on Wednesday.

"For everyone's safety, because it could be such a big storm ... we want to be ahead of it," New York Mayor Bill de Blasio said on Tuesday.

In New Jersey, Governor Phil Murphy on Tuesday declared a state of emergency, with state offices as well as schools in many districts closed.

Both the Greyhound bus and the Amtrak passenger train services suspended or abbreviated routes for the day. Throughout the East Coast, local bus and train operators that millions of people rely on to commute to and from work and school also canceled service on Wednesday.

Widespread power outages were expected as heavy snow and ice along winds may topple trees and power lines, the National Weather Service said.

Already, about 28,000 electricity customers were without power in Virginia and West Virginia.

Across the country in Southern California, residents of Santa Barbara County were bracing for heavy rains forecast to hit the region this week and potentially trigger mudslides.

Authorities on Tuesday ordered thousands of Santa Barbara County residents to evacuate as a precaution, after 21 people were killed and dozens injured in mudslides on the area on Jan. 9.

The East Coast storm, the fourth winter blast of snow and wind this month, was dubbed a "four'easter" by some news media outlets. It followed storms on March 2, 7 and 12 that left at least nine people dead across the region and more than 2 million homes and businesses without power.

(Reporting by Alex Dobuzinskis in Los Angeles, Alana Wise and Scott DiSavino in New York, Bernadette Baum in Montclair, New Jersey, Suzannah Gonzales in Chicago, Keith Coffman in Denver, and Brendan O'Brien in Milwaukee; Editing by Amrutha Gayathri and Jonathan Oatis)