Another day, another precarious weather forecast for New Jersey.
A winter storm is expected to plow through the Garden State from Sunday night into Monday, bringing a combination of heavy snow, ice and rain that could snarl morning commutes, forecasters said.
The National Weather Service issued winter storm warnings from 7 p.m. Sunday through Monday in areas north of Trenton that could see heavy snow and ice, while winter weather advisories are in place in southern New Jersey, where more rain is expected.
Who gets what and how much is no simple question to answer.
While the focus during last week's potential blizzard centered on where the storm would form and track, the rain/ice/snow line is the forecaster's conundrum this time around.
"It's the forecaster's nightmare ... this is turning out to be the classic New Jersey winter storm potpourri," said David Robinson, the state climatologist at Rutgers University.
As of late early evening Sunday, forecasters said areas north of Interstate 80 will likely see snow for the duration of the storm, and as much as 10 inches is possible before the storm pulls away from the region Monday.
Between I-78 and I-80, from 3 to 6 inches of snow may fall before precipitation transitions to sleet and/or freezing rain, which could last through the morning. Upwards of a quarter of inch of ice is possible, enough to cause major issues on the roadways and could impact tree limbs and power lines.
While some snow is expected farther south, enough warm air is expected to push into the state to change precipitation to rain by sunrise, which should lessen impacts on travel Monday.
Roadways could quickly deteriorate because cold air has been in place at the surface for several days.
"It's going to get pretty nasty," said Walter Drag, a meteorologist at The National Weather Service in Mount Holly.
Forecasting precipitation type is often a challenge in New Jersey because it is often a battleground for the freezing line during winter storms. Meteorologists must not only monitor conditions at the surface but vertically throughout the atmosphere in a fast changing environment - the slightest twinge in temperatures anywhere could mean a world of difference in what type of precipitation falls.
"They really have to be forecasting through four dimensions - it's temperatures at any given area in the atmosphere and at the surface as it changes through time," Robinson said. "It would almost be easier if nothing but a fluffy snow were forecast."
The storm is expected to push warm, southerly air into the region as it tracks across the state. Where that air makes it to the surface, rain will fall. Where cold air dominates -- likely in the northern-most sections of the state -- snow will fall.
It's the zone in-between that's the trickiest. In central New Jersey, cold air is expected to hang on at the surface while temperatures are expected to rise above freezing in the mid-levels of the atmosphere. As snow develops and falls from the upper-reaches of the atmosphere, it melts as it encounters this warm layer but refreezes when it encounters thte colder air near the surface.
The result is either freezing rain or sleet.
"Now the question is, where does that mixing line go?" said Sam DeAlba, a meteorologist at WeatherWorks in Hackettstown. "How long do these places hang onto snow? Those places that see snow, sleet and freezing rain, it's going to get very ugly on the roads."
The storm is also expected to be followed by a blast of cold air, which may change precipitation back to snow for the entire state Monday afternoon. Wind chills will likely fall below zero Monday night for much of the state while temperatures will likely drop to the single digits or teens, which could cause a flash freeze on untreated surfaces.
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