I’ve seen the CCB slam SE areas including the Cape and this sort of mini slot develops in srn RI and into extreme SE CT. Maybe into areas west of New Bedford too. It’s definitely the dryslot in the mid levels, but sometimes the CCB from 850-700 can mask that off to the east. Sure maybe the prime DGZ dries out, but you have a firehose of moisture and small to medium sized flakes there.
It doesn’t happen in every storm, but besides the March 2013 event, January 2005 and I remember January 2011 was an issue there too.
It’s not due to downsloping, but perhaps maybe a standing wave that can develop if conditions favor. That’s what happened in March 2013 to the extreme. Big isentropic lift or upglide in ern areas. Sinking air to the point that sun sun was visible in RI, and then upglide again in CT. There was also a s/w in NY state that likely aided the totals near Kevin.