What causes the dark streaks on the roof of one side of your house?

When hail stones hit your roof, it punches through the integrity of shingle tabs, exposing the tar sheets underneath. From this time onward, whenever it rains, tar will seep out from these impact points to create these dark streaks. Insurance companies would like you to believe that it is mold but it is not. If it were mold, then it would be on all roof slopes. They appear on roof slopes facing a certain direction, because when hail falls, it falls at a consistent angle. Roof slopes most perpendicular to the paths of the hail stones will receive the deepest damage of hail stones and most dark streaks.