My Personal Weatherman™
12km NAM showing big snowstorm for Long Island:
We aren't within range of the higher-resolution NAM, but the 12km NAM goes out 84 hours, and it's showing the snow starting on Long Island around midnight Sunday night and going into at least Monday night when the run ends. It's only showing some rain for the south fork Monday evening. When the run ends at 7 PM, it already has 7 to 10 inches for Long Island if you look at the positive snow depth change map, and it's showing 10 to 15 inches if you look at the 10:1 snow map.
This video goes from 10 PM Sunday to 7 PM Monday: