Well it’s really unstable in lower levels. You have cyclonic flow so enough moisture aloft, and I think some convergence along a front and with LLJ. You can see this on the NAM.
Nice little event there. It was modeled well by Reggie and I noticed today some other models had it which is why I mentioned that one band north of pike. Might leak over to Methuen and save some gifts from going into the Merrimack.