In the (Mt Washington) Valley - halfway between us - it went 2-4' in spots with no snow cover to the normal 2-3' where there was plenty of insulation from 3-5' of snow. Info from buddy who operates one of those giant excavators down there. You had more snow in Ossipee, higher temps, we had less snow in Gorham, colder temps. I would say frost went at least 3' deep in my back yard. Parsnips will be late digging here. But I doubt frost got much below 2' down there except under roads and parking lots.
How thick did the ice get on the lakes?