Here’s a link to the skew-t from New York. (closest I could find to New Jersey). A skew-t is a diagram of the temperature and dewpoint at different heights in the atmosphere. It comes from good old-fashioned weather balloons.
This skew-t shows that the surface temp was below freezing, but that there was a warmer layer aloft, from approx. 800 feet to 2,500 feet. So falling snow would melt in the warm layer, then have just enough time to re-freeze as it falls through the lowest layer (800 ft and down). If it was a little colder at the surface, and a little warmer aloft, you would have gotten freezing rain. If the warm layer was a little lower and shallower, you would have gotten a mix of rain and snow.
Of course the skew-t just represents one moment in time. As a front moves through, the temps at different layers can change rapidly and you get grab bag weather. As a forecaster, I’m fond of using the term “wintry mix.” Yah, it’s waffling, but now maybe you can see why I need to waffle sometimes.
By the way, the link above probably links to the most current skew-t, so people coming to the thread after this afternoon might be seeing a different picture.
That’s probably more than most people want to know about skew-t’s, but in case anyone wants more info, here’s a link to Penn State Weather Dept.