The early observations, and final rainfall totals really showed the topographical effects of this event.
It was a textbook SE flow orographic event that coupled with favorable upper level dynamics.
High moisture levels (high dews and PWATS), abnormally strong prolonged moisture transport, with the NWS noting closed circulations aloft over western NY as the event developed... that just funnels moisture from the Atlantic up into the terrain reaching from western CT/adjacent NY northward through the eastern slopes of the Greens.
In Vermont, there was low level orographics coupling with favorable upper level lift that took this precipitation event into historic levels. Just a wave of moisture into the terrain off the Atlantic, with peak efficiency occurring on the east slopes like a blocked flow. Best lift was upstream of the barrier and in the zone of rising air out of the upper CT/White River Valley.