Warmer and moister air from the south will push over a warm front tonight. The rising air will cool and produce snow. This snow is already happening above us now. The air just above the ground is dry, so the snow is sublimating before it gets to the ground.
How much snow anyone gets will depend on how quickly the warmer air moving at the surface. Warm fronts are less well defined and the warm air has to push out the denser cold, dry air. The National Weather Service is expecting that to happen and change the snow to rain, with some moderately heavy rain, by early morning. A coating of snow for NYC and an inch for Westchester and Rockland and nearby Connecticut is the most likely outcome.
Forecasts with warm front snow have less certainty that cold fronts or coastal storms, so be ready; if the change over is delayed, a period of freezing rain could occur before sunrise.
Here’s the NWS forecast discussion from early afternoon…..
However, if temperatures at the surface closer towards the coast, such as Rockland, Westchester, Eastern Passaic, Western Essex, Western Union, trend just a few degrees colder for overnight, the wintry mix would include freezing rain with a possibility of the winter weather advisory getting expanded. However, recent model runs, such as the NAM12 continue to show temperatures and even wet bulb temperatures a few degrees above freezing for the precipitation overnight into Monday morning. So, confidence of any ice accumulation is lower because of this but a chance of freezing rain is in the forecast.