Grubs are dormant in winter. Whatever you’re seeing, it isn’t grub damage (unless it was already there last fall). A fungus called snow mold can attack lawns underneath a snow cover. Did you notice any matting or webbing as the snow melted? Without seeing a sample, that’s just a guess. Take a sample of the affected grass to a garden center or county extension service to see if it’s snow mold or something else. If it is snow mold, the turf may recover on its own. The fungus depends on temperatures just above freezing and high humidity for survival. So as the lawn dries out and air temperatures warm up, the problem should go away. If the infestation is not severe, the crown (growing point) of your grass may have survived and will sprout new growth once conditions improve. Help it along by vigorously raking the patch to allow more oxygen to reach the crowns. In severe cases, patches of grass may be killed. In that case, overseed or sod the dead areas.