HARTFORD, Conn. — Residents of several major Northeast cities are experiencing a fast-moving coastal storm that is bringing a mix of sleet, rain and snow to areas along the busy Interstate 95 corridor this weekend.

The snow that began falling in southeastern Pennsylvania and West Virginia late Friday had become rain and sleet in some areas by early Saturday, and the National Weather Service said Washington, D.C., Delaware and most of Maryland had rain. But conditions in some locations were expected to worsen as the day progressed.

Southern New England could get walloped with the largest amount of snowfall, but temperatures hovering near freezing could make for slippery driving conditions across the region, forecasters warned.

“It’s kind of the first one, so it’s a good thing it’s happening this weekend,” weather service meteorologist Bill Simpson in Taunton, Mass., said Friday of the storm. “If this happened during a weekday, it could be really slow and messy.”

A winter storm warning was issued Friday for a large portion of central Pennsylvania ahead of the storm. Forecasters said a wide area between Gettysburg and Johnstown, stretching from West Virginia through Maryland to just south of State College and Williamsport, could get 5 to 8 inches of snow by Saturday afternoon.

The Maryland State Highway Administration warned motorists that travel may become hazardous.

As the storm moves northeast along the seaboard, it is expected to drop 2 to 4 inches of snow and ice in Philadelphia on Saturday before turning over to rain. It is forecast to bring 3 to 4 inches of snow to New York City.

Boston Mayor Martin Walsh issued a statement urging residents to help the city’s vulnerable populations, particularly the elderly and homeless.

“We ask that each and every single Boston resident look after their neighbor, be it someone you see outdoors or someone living next door,” he said.