With my goal of hiking all the NH 4k footers with my father-in-law completed, I've set a goal of hiking all 67 New England 4k footers in and out of Winter. Previously all my hikes have been in either the summer or fall. That means the entire trip must begin after the hour and minute of the beginning of winter (winter solstice) and end before the hour and minute of the end of winter (vernal equinox).
AMC 4000 footer FAQ