Late Monday, some of the well-respected computer models were arguing for totals at the lower end of the forecast range. "There's still a little wobble and disagreement," said Dean Iovino, a meteorologist at the weather service's Mount Holly office.
But a significant snowfall, driven by icy winds, followed by a frigid workweek, was all but a certainty.
"Believe me, it's coming," said Alex Sosnowski, a meteorologist at AccuWeather Inc., which was predicting three to six inches.
Snow was expected to arrive before noon, become heavy by midafternoon, and continue well into the night. Temperatures will head south through the 20s - 25 to 30 degrees colder than Monday's high.
"People are going to step outside and go, 'What the heck!' " Sosnowski said.
The storm is a "clipper," one moving west to east across the country, riding the tremendous temperature contrasts along an Arctic front. As the front has sagged southward, anywhere from six to eight clippers have raced across the country in the last 10 days, said Sosnowski, and one was due to blow up.
That would be this one, something computer models failed to pick up until Sunday night.
The storm is expected to get a kick from Atlantic moisture as it approaches the Carolina coast, and, Sosnowski said, near-blizzard conditions are possible in parts of Central New Jersey.
The forecast meant a now-familiar drill for highway departments on both sides of the river. The Pennsylvania Department of Transportation already has gone through more than two-thirds of its total seasonal snow-fighting budget, and the New Jersey department has spent more than twice what it did during the entire winter of 2011-12.
Temperatures are forecast to fall into the single digits Wednesday, which would complicate the cleanup. Shoveling is not a pleasant exercise when wind chills are below zero, and road salt becomes less effective in pavement temperatures below 15, said Nick Martino, a PennDot maintenance manager.
One break plowing crews will get is that this won't be a wintry mix, but a powdery snow purified by frigid temperatures.
The winter of 2013-14 had already produced two six-inch-plus snowfalls by Jan. 3, something that had never occurred so early in Philadelphia.
The seasonal total stands at 20.2, about two inches under the average for an entire season.
A final note: The typical peak snow period in Philadelphia is about a week away.