The single most important thing to look for is cold air. If you get that over warm lakes you get clouds and thus lake effect. Everyone's definition of a "big time" event is different. For us in lake effect belts our definition is somewhere around 30-35"+ from one single event. In other regions that is virtually unattainable. Many posters even in this sub forum may have a different characterization of what a big event is. Many include wind, temp, wind chill, snow depth into the factoring of what is considered a big event.
A large event for me would be 1-2' of snow. A big time event 30"+