Tonight / Tomorrow

***Winter Weather Advisories have been issued for Southern and Central NJ and Winter Storm Watches have been issued for the Poconos and NW NJ***

Our system that will be moving in tonight and spreading snow over the region is on track. Snow should begin in the early morning hours on Saturday. Snow will accumulate rather rapidly since 1. It is nigh time and 2. Highs today will be in the 30's. I would expect most areas to have the ground covered by the time you wake up.

This storm will be driven by the infiltration of warm air into the atmosphere. This process is known as Warm Air Advection. These types of  storms are very tough to get an all snow event here. Why you may ask? The simple answer is, the entire column that precipitation falls through at the onset will be cold enough to support snow. As warm air moves in, part of the column will potentially go above freezing. This will cause the precipitation to either change to sleet, freezing rain or rain. If the warming occurs in the highest levels, the precipitation will melt and then refreeze as it falls closer to the ground (the result would be sleet). If the warming occurs closer to the ground, but the surface is still below freezing, this would result in freezing rain. And obviously, if the entire column and ground are above freezing, the result is rain.

So, the entire storm is going to hinge on how fast the warm air advects into the region. The sooner, more mixed precipitation, the longer, the more snow. There is no question warm air will invade, the question will be how fast. Typically, with these systems, it will advect earlier, so I am thinking things will switch over sooner rather than later. The question will then be, for how long do we have mixed precipitation. 

What I am thinking now is:

1. Areas between Philly and Trenton will receive 1-3" of snow. The snow in this area will transiion to sleet and freezing rain, and may have significant icing before possibly changing over to all rain..

2. Areas from North of Trenton to NYC will receive 2-4" of snow and then transition over to a mixed precipitation event for the remainder. Significant ice accumulations possible.

3. Areas from the Poconos to just north of NYC to north of 95 in CT will be all snow, and accumulations will be on average from 4-8"

Regardless of what falls, Saturday night may be downright treacherous. Temperatures are expected to tumble below freezing, so any liquid will freeze.

More updates as needed!