Ady, my criteria for a day sailed in my "windsurfing season in Iowa" is any day I sailed using a windsurfing rig (universal joint, mast base, mast, boom & sail) on a board (windsurfer, or a board with wheels, skis or blades) that moves me across a surface (fluid water, asphalt, cement, ground, packed snow, or ice) in Iowa. As of January, 2018 my months in a row is 287 (March 1994 to now).
My wintertime sessions are much shorter than the rest of the year. They go like this: at the site keep the van running, put several sets of mittens on dash getting the full heater/defroster treatment, unload board or sled, rig sail, attach rig to board, adjust everything so the wind won't blow it away, get back in the van, put on elbow & knee pads and motorcycle helmet, take one set of mittens off dashboard and put them on, turn off the van, get out and sail until fingers are too cold, return to van, restart & run van using heater/defroster to re-warm the just used mittens, when hands are warm put on the 2nd set of warmed mittens, turn off the van & sail again. This time the sailing will last longer because hands stay warm longer the 2nd time. Keep repeating the hand warming cycle as needed. Maybe the first sail time is only 10 minutes, if so the 2nd one will be about 30 minutes. I usually alternate 2-3 pairs of mittens.