I noticed a week or two ago patterns forming on my glass when it rains. I wanted to get a picture but I didnt think it was too safe jumpimg into the backseat on the highway lol. The image below is what I observed. The blue shaded area stays completley dry. The red lines represtents the water flowing down the glass in little rivers. As you get closer to the center of the vehicle the lines pull in closer to the centerline starting approximatley 1/4th of the way down then they pull back out towards the outside edge again as depicted in the photo I provided. The area in between the red lines appears to be a film of water that can be dificult to see through. The water in those areas appears to be pushing in toward the redlines combining I would imagine with the water coming off the roof. There is also a small semi-dry almost speckled area near the top of the glass represented in yellow that must be where the the air separates from the vehicle.
I dont know what info I am looking for with this post I just thought the aerodynamics at play here were interesting.
Dean