The latest ever first snow in NYC occurred on January 29, 1973. Source: New York City's snow drought nears all-time record | AccuWeather
This market resolves YES if the first snow of this year is on or after January 30. It will resolve NO otherwise, including if the first snow is on January 29 itself (this market is about BREAKING the record).
The official location of snowfall measurement is Central Park. This will be covered widely in the news so this should not be ambiguous to resolve.