You may be sick of the slushy stuff, but at this Saturday’s WinterJam, which moves from Central to Prospect Park this year, you’ll find a field of freshly groomed powder for skiing, snowshoeing, and other wintry shenanigans. Pros will be on hand to give ski and snowboard lessons, and everything, even equipment rental, is free (the Nethermead in Prospect Park; 718-965-8951; 11 a.m. to 4 p.m.).