Roof Leak - Valley Debris Build Up.
At least once a year the valley's on your roof need to be cleaned out. The valley is that part of your roof where water is supposed to drain all the way to the ground. The valley needs to be clear of dirt, leave, twigs, etc.to be sure that the water dosen't backup over the flashing and find it's way onto a ceiling below. If you do have this problem where a significant amount of water has leaked into the attic, don't forget to have the wet insulation replaced. During colder months it will not dry out and it will become a breeding ground for mold.