I talked to my neighbor today on the way home (for the first time .. he's only lived there about 6 months or so). He seems like a nice guy and readily admitted that the arrow was probably his. He recently bought a new scope for his crossbow and was sighting it in last week. He shot at his ground mounted target (like about a 2 foot cube) from his back porch and the arrow skimmed off the top and launched upward and he lost it. I fired up google earth and compared the position of my front porch and his back porch and it looks ...doable. It's about 330 yards between the 2 locations, but heavily wooded. Looking at the angles, if the arrow stayed above the trees and didn't hit anything the arrival angle in my roof pretty much matches that angle I saw. I thought it would not have been anywhere close.. but it is, due to the orientation of the houses and the curvature of the road.
I have no 'feel' for crossbow arrows and the distance involved, but with the right tail wind (and we did have some pretty decent winds going along the edges of Eta as it came by somewhat north of us), it seems like the arrow 'spent itself out' going skyward and then, more or less FELL to the earth ..uh.. my roof. The distance between our houses is only about 20 yards further than the length of my driveway .. so almost a perfect isosceles triangle between the road, my driveway and the flight of the arrow (yellow line). Oh.. and I'm guessing that the elevation of my house roof is just about equal to the elevation of his back porch (and target).
Steve