So, ignoring the recent no snow situation and looking at it from a 30+ year period of living in the Monadnock region (so my experience),
I'd revise that to
4-8" ordinary
6-12" also ordinary but a pleasant bonus
12-18" impactful but other than school closing, not much else unless the power goes out
18-24" impactful, power will probably go out for some reason
24" - major