BOSTON >> A snowstorm that started in the predawn hours today was expected to bring up to a foot of accumulation in some areas of the U.S. Northeast by the time it ends late in the day, while other spots were contending with a sloppy mix of sleet and ice.

The National Weather Service issued a winter storm warning for most of New England and eastern New York, and a winter weather advisory stretching from Ohio into coastal areas of southern New England and northern Maine.

By mid-afternoon, some areas of New England have already received 9 to 10 inches of snow, and the weather service warned of a flash freeze in the evening hours as temperatures dropped from the low 30s into the low 20s, causing wet roads to freeze over, making driving dangerous.

Governors across the region urged residents to stay off the roads if possible, and to slow down and keep a safe distance from plows if driving.

“If you don’t have to travel tomorrow, we urge you to consider staying home, and if you do need to travel, please use caution throughout the day,” Massachusetts Gov. Charlie Baker said in a statement late Thursday.

Major airports across the region reported hundreds of outgoing flight cancellations, including more than 300 at Boston’s Logan International Airport and more than 100 at Newark Liberty International Airport in New Jersey.

With travel treacherous, the New York State Thruway temporarily reduced the speed limit to 45 mph across a large stretch of the highway this morning, and the speed limit on the Massachusetts Turnpike was reduced to 40 mph.

Police reported multiple accidents. Massachusetts State Police reported a jackknifed tractor-trailer on the Braga Bridge in Fall River, and a tractor-trailer rollover on the Massachusetts Turnpike in Auburn.

Slick roads caused by the weather were blamed for four traffic fatalities in Missouri, the Missouri State Highway Patrol said. The victims included a 74-year-old Warsaw woman who died today after a Thursday crash on Interstate 44 near St. Louis. The car she was a passenger in was going too fast for wet road conditions when it hit a concrete median barrier.

The other victims were an 18-year-old man from Ballwin, a 52-year-old man from St. Peters and a 54-year-old man from Ashland.

Commuter rail service was temporarily suspended on a section of New Jersey Transit’s Morris and Essex Line after a tree fell on overhead wires in Chatham.

A commuter train was delayed in Massachusetts when it struck an unoccupied sidewalk snowplow that had been left on the tracks in Waltham. No one was hurt.

Public school children in many Northeast states were on vacation this week, but schools and colleges that were still open opted to either cancel classes for the day or make today a remote learning day.

Ski areas cheered the fresh snow that came after unseasonably warm temperatures earlier in the week.

“Mother Nature is officially confused as to how to spend her time, but she seems to have a great short-term plan for now,” Mad River Glen in Fayston, Vermont, said on its website today.