UPDATE: Snow late in arriving, but 4 inches still expected for much of N.J.

The exact timing of the storm is not set in stone, but it's looking likely that Old Man Winter will be making a mess of Friday morning's commute in northern and central New Jersey.

A storm system that's approaching New Jersey is expected to bring some light rain to the region late Thursday night and in the hours just after midnight, forecasters say. The bad news: As colder air flows in from the north, temperatures will be dropping near the freezing mark and the rain will quickly change to snow.

And forecasters say there's a strong possibility that the heaviest snow will fall during the morning rush hour.

NJ Transit officials warned commuters that plans to operate trains and buses on a regular weekday schedule could change as conditions worsen. Tickets will be cross honored between the agency's trains, light rail and buses on Friday. Riders are being asked to monitor NJTransit.com for information.

Projected timing

Light rain is expected to overspread the I-80 corridor in northeastern Pennsylvania and northwestern New Jersey between 8 p.m. and 11 p.m. Thursday, then gradually expand south and east during the overnight and early morning hours, according to the National Weather Service.

Friday morning SNOW! March Madness begins now! Gonna be a sloppy morning ride to work. @news12nj #njmorningshow pic.twitter.com/nGVueoZVDE — James Gregorio (@JamesGWeather) March 9, 2017

Central and eastern counties will likely see the initial rain starting after midnight and changing over to snow between 2 a.m. and 4 a.m., said Valerie Meola, a meteorologist at the National Weather Service's regional forecast office in Mount Holly.

The changeover from rain to snow should be fairly quick, Meola said, so there shouldn't be a long period of sleet or freezing rain.

In South Jersey, the switch from rain to snow will probably occur between 5 a.m. and 8 a.m., Meola said, keeping snowfall accumulation very low in that region.

Most of the snow should be over by the early afternoon on Friday, although there could be some isolated snow showers or snow squalls -- pockets of brief heavy snow.

Frigid air

As the storm system moves away from New Jersey, even colder air will be sweeping in, along with gusty winds. Temperatures Friday night will be dropping into the teens, the weather service said, so any snow that doesn't melt before then will turn to ice.

Snowfall projections

As of late Thursday afternoon, the National Weather Service is predicting this much snow to accumulate across New Jersey by Friday afternoon:

Sussex, Passaic, Bergen, Essex, Hudson and Union: 4 to 6 inches.

Morris and Warren: 3 to 4 inches.

Hunterdon, Somerset, Mercer, Middlesex and Monmouth: 2 to 3 inches.

Burlington, Camden, Gloucester and Ocean: Less than 1 inch.

Atlantic, Cape May, Cumberland and Salem: Less than 1 inch.

Note: If these projections change Thursday night, they will be updated.

Here's how much snow the National Weather Service is predicting from Thursday night through Friday afternoon. This map was updated Thursday afternoon. Counties in northeastern New Jersey are included in the map below. (National Weather Service)

Storm alerts

As of late Thursday afternoon, the following storm advisories were issued by the National Weather Service offices in Mount Holly and Upton, N.Y.:

Sussex County: A winter weather advisory is in effect from 8 p.m. Thursday to 10 a.m. Friday.

Bergen, Essex, Hudson, Passaic and Union: A winter weather advisory is in effect from 10 p.m. Thursday to 2 p.m. Friday.

Hunterdon, Mercer, Middlesex, Monmouth, Morris, Somerset and Warren: A winter weather advisory is in effect from midnight Thursday to noon on Friday.

Here's how much snow the National Weather Service is predicting from Thursday night through Friday afternoon. This map was updated Thursday afternoon. (National Weather Service)

NJ Advance Media staff writer Larry Higgs contributed to this report. Len Melisurgo may be reached at LMelisurgo@njadvancemedia.com. Follow him on Twitter @LensReality or like him on Facebook. Find NJ.com on Facebook.