Significant snowfall could create perilous driving conditions for the Friday morning commute.A sweeping weather system was producing snow across parts of the Northeast and the Mid-Atlantic early Friday, creating dangerous driving conditions and potentially snarling the morning commute for millions, some of whom were slammed by a significant snowstorm earlier this week.Across the Northeast, snow was expected to fall at a rate of at least an inch per hour, and potentially more rapidly across eastern Long Island and southeastern Connecticut, the National Weather Service in New York said on Thursday night. New York City could see up to five inches of snow, and up to seven inches could fall on Long Island.By early Friday, as snow began to blanket the area, air and roadway temperatures were near or below the freezing mark, the Weather Service said, adding that travel had become “treacherous.”Winter weather advisories were in effect across the New York metropolitan region, and storm warnings indicating more severe conditions were in place for Suffolk County on Long Island, Middlesex County in New Jersey, and New London County in Connecticut.As of 5 a.m. Eastern, hundreds of flights out of La Guardia Airport and John F. Kennedy International Airport in New York were either canceled or delayed, although it was unclear if the disruptions were because of winter weather or the stress caused to the industry because of the recent surge in Covid-19 cases across the United States. Several flights out of Dulles International Airport in Washington were canceled Friday morning, while Amtrak announced at least two train cancellations departing from New York.In New England, winter storm warnings were issued for most of eastern Massachusetts and nearly all of Rhode Island. Farther north, a portion of Maine was under a blizzard warning.Winter Storms in the United StatesFrom the East Coast to the Western U.S., a barrage of winter storms has wreaked havoc across the country.Virginia: Hundreds of drivers were stranded for more than 24 hours after a snowstorm brought I-95 to a standstill near Washington, D.C.Colorado: Days after a catastrophic fire destroyed hundreds of homes near Boulder, residents were hit with nearly a foot of snow.Widespread Power Outages: More than half a million customers were left without power in the Southeast and Mid-Atlantic.Travel Disruptions: Covid-related staff shortages and the storms have led to thousands of flight cancellations.The Washington area, slammed just days ago with more than eight inches of snow, was expected to get another round, with the National Weather Service forecasting up to four inches. Federal offices in Washington would be closed on Friday, officials said.Some school districts along the Interstate-95 corridor, already facing growing concerns amid rising Covid-19 cases, adjusted their operations for Friday. Mayor Muriel Bowser of Washington announced that schools would be closed because of the storm. Public schools in Philadelphia were shifting to remote learning while several districts in New Jersey were either closing for the day or were operating on a delay. New York City public schools would remain open, officials said.The new storm system comes on the heels of a wintry wallop that coated roads with snow and ice, setting new daily snowfall records, knocking out power for a half a million people, jamming roads for miles and stranding drivers overnight in their cars along Interstate 95 south of Washington.New York City and New Jersey on Thursday announced preparations for the coming snowfall and warned of hazardous travel conditions and potential weather-related delays.New York City Emergency Management was activating a virtual situation room to monitor the storm system and had issued a travel advisory for Friday. Mayor Eric Adams said his team would convene at 4 a.m. Friday to review the city’s storm response and “direct resources where needed.”.At a news conference on Thursday afternoon, Gov. Phil Murphy of New Jersey declared a state of emergency to begin at 10 p.m. and urged residents to stay home if they can.“If you can work remotely tomorrow or report later than usual, you may wish to take those options and stay off the roads,” Mr. Murphy said.The storm system, which the National Weather Service called a “quick moving but intensifying low pressure system,” has already left a trail of freezing rain, snow, and sleet across a swath of the South, including Tennessee and Kentucky.