When the crowds stop coming the mountains close. With small crowds and discounted lift tickets and the majority of the customers, season passholders ski areas don't make the kind of revenue in the spring that they make in mid winter. If early spring is abnormally cold and crowds show up some resorts may be open for a bonus weekend. Killington and Sunday river seem to be the only resorts that try to stay open into May. Most shutdown around early to mid April which really isn't that bad.