UPDATE: N.J. school districts announce delayed openings for Tuesday, Dec. 17

First things first. This will not be a blizzard. This will not be a major winter storm that dumps huge amounts of snow on the Garden State.

But forecasters say the storm system that’s moving from the Tennessee Valley and across New Jersey could be a dangerous one, because it has the potential to create a slick coating of ice on roads, sidewalks, tree branches and power lines — particularly in the northern third of the state.

That’s where temperatures at different levels of the atmosphere will be fluctuating below and above the freezing mark, resulting in a wintry mix of snow, sleet, plain rain and freezing rain.

When rain falls on surfaces where temperatures are at or below 32 degrees, those droplets quickly turn into ice, creating what’s commonly known as freezing rain.

Forecasters are worried some areas of New Jersey could end up with an icy coating of one-tenth to one-quarter of an inch on top of any snow or sleet that accumulates. That’s a bad recipe for driving conditions and also could trigger scattered power outages from snapped tree limbs and power lines.

Here’s what forecasters are predicting in terms of the storm’s timing and how much snow and ice is likely to accumulate.

MONDAY AFTERNOON

Although weak bands of rain and snow flurries moved through parts of the state Monday morning and into the early afternoon, most of New Jersey will be dry during the start of the evening rush hour, said Jim Sullivan, a meteorologist at the WeatherWorks forecasting company.

However, some areas will see a few sprinkles or flurries.

MONDAY NIGHT

A second wave of precipitation will likely arrive in central and southern New Jersey after 5 p.m. or 6 p.m., then move into northern New Jersey by 9 p.m. or 10 p.m., Sullivan said.

“The evening rush hour should be in fairly decent shape,” he said. “During the tail end of it, maybe we’ll see some sleet or snow that causes a few minor delays.”

The types of precipitation will vary depending on your location. Sullivan expects the dividing line to be generally near Interstate 78, with areas north of the highway getting several hours of accumulating snow Monday night.

Areas along and south of Interstate 78 will likely get a short period of snow, sleet and freezing rain Monday night, changing to plain rain as warmer air works in, Sullivan said.

“The farther north you go, generally more snow” will fall, he said, noting high-terrain areas of Sussex, Morris and Passaic counties — primarily north of Interstate 80 — could get 2 to 4 inches of snow.

Update (4:40 p.m.): Sussex and Warren counties had been under a winter weather advisory Monday morning, but the National Weather Service upgraded the advisory to a winter storm warning at 3:30 p.m., effective until 6 p.m. Tuesday. The weather service is calling for 2 to 4 inches of snow, plus up to a quarter-inch of ice, in those areas of the state.

“Plan on slippery road conditions,” the weather service said in its storm warning. “If you must travel, keep an extra flashlight, food, and water in your vehicle in case of an emergency.”

TUESDAY MORNING

Around midnight and into the early-morning hours on Tuesday, areas of northern New Jersey that are getting snow will likely see the snow change over to sleet and freezing rain, Sullivan said.

In places along Interstate 80 and north, especially in hilly areas, freezing rain could linger into the Tuesday morning rush hour and perhaps into the late afternoon.

“It could become a full-blown ice storm for some parts of that area,” Sullivan said.

Varying amounts of ice are expected in the transition zone, between Interstate 80 and Interstate 78, but not much ice is expected in areas south of Interstate 78, Sullivan said.

TUESDAY AFTERNOON

In areas north of Interstate 80, the precipitation — rain or freezing rain at this point — should wind down between 4 or 5 p.m. Tuesday, Sullivan said. For areas south of I-80, it should be in the form of rain, which should taper off from west to east between 3 p.m. and 6 p.m.

TUESDAY NIGHT

The NationaI Weather Service is calling for a chance of lingering rain showers or snow showers Tuesday night, but no additional accumulation is expected. Temperatures are forecast to drop into the upper 20s to low 30s by Wednesday morning, when skies will clear, but winds become gusty.

Len Melisurgo may be reached at LMelisurgo@njadvancemedia.com. Follow him on Twitter @LensReality or like him on Facebook. Find NJ.com on Facebook.