I have an issue I cannot solve. About a month ago I was checking things in my attic and noticed some frost on my attic sheathing. The interesting thing is, the frost is only above my stoop; there is no other frost on the sheathing anywhere. I crawled over and noticed the stoop is covered in a few inches of blown in insulation apparently on purpose. The stoop ceiling is soffit ventilation. The stoop is facing the northwest so could it be wind blown moisture thru the soffit? Should I seal the stoop soffit or add insulation to block the cold air? I can't figure this one out and need some advice...I will add that all major air leaks have been sealed and I have added insulation to reach R-50.