Synopsis
A very active weather pattern this month brings yet another chance for decent accumulations of snow in NYC. This storm will be on the weaker side, and will slow down as it tracks offshore of the region. The result should be a long duration but likely a generally light to moderate snowfall event. Snowfall totals around NYC will probably be in the range of 4-6″, though with every storm this season, some potential exists for both higher and lower totals. If colder scenarios and better lift are realized, we could see > 8″. A warmer scenario would see more mixing and totals below 4″. Light snow should spread over NYC during the afternoon hours with periods of moderate and potentially heavy snow in the early evening. Mixing with sleet and rain even is possible during the early overnight hours. Snow and sleet could continue into the early afternoon hours Friday.
Weather Prediction Center 48 hour median snowfall accumulations for the NYC metro region ending 7PM Friday. This is showing about 4-6″. 
Weather Prediction Center 48 hour 90th percentile snowfall accumulations for the NYC metro region ending 7PM Friday, showing 6-8″. 
GEFS ensemble plumes for total snow accumulation at KLGA. The mean here is about 7″ with a significant spread among ensemble members both higher and lower than this. 
SREF ensemble plumes for total snow accumulation at KLGA. The mean is about 5.5″, with similarly large ensemble spread..
Forecast Details
At the Surface
Deep arctic air precedes this storm, which will form along a frontal boundary stretching from the Gulf Coast to offshore of the Mid-Atlantic. This low will be on the weak side, only hitting around 1012-1000 mb. For reference, the last couple storms that hit us were about 10-15 mb deeper. Over the course of the week, models have trended colder with the storm, pushing its trajectory further offshore, close to or outside of the 40ºN 70ºW benchmark that signals the best snowmaking potential for NYC during coastal winter storms. It is important to note that even with the track trending colder, mixing is still likely at some point during the storm, and significant mixing would lower overall totals. If we have an overall colder scenario, we may see closer to 8″ by this time Friday.
ECMWF “Euro” model surface precipitation/type at 1PM Thursday. 
GFS model 1000-500 mb pressure, thickness, and surface precipitation/type at 7PM Thursday. 
NAM model 1000-500 mb pressure, thickness, and surface precipitation/type 1PM Thursday. 
Weather Prediction Center storm track forecast.
850 mb Level
There isn’t a strong sign of a robust 850 mb low-level jet with this storm. That’s in line with the profile of a weaker storm with less intense precipitation. However, most models do show the 850 mb warm nose setting up just south of the city, which would favor the strongest precipitation occurring as mostly snow over the city during the Thursday afternoon-early evening time frame.
NAM model 850 mb winds and relative humidity at 1PM Thursday. 
GFS model 850 mb temperature, height, wind at 1PM Thursday 
ECMWF “Euro” model 500 mb height & vorticity at 1PM Thursday
500 mb Level
A longwave trough that reflects the very cold air over the central part of the US will be in place upstream of this low. There will not be any negatively tilted trough at this level providing enhanced lift for this low, thus explaining the weaker profile of this storm.
300 mb Level
Similarly, the best support for strong lift at this level of the atmosphere won’t come until late in this storm’s evolution. There are no clear entrance or exit regions co-located with the storm early on, signifying an absence of enhanced lift from divergence at this level.