In bad weather the rear window is always dirty and requires continual cleaning using the wiper. I have had several vehicles which have rear wipers that are not really needed. However the airflow behind the Tahoe Hybrid during bad weather really requires the use of the rear wiper.
If you do not use it during heavy snow it will not clean the window resulting in a stop to clean it.

 

its an areodynamic low pressure area....

 

Back in the day, there were air deflectors, typically attached to the roof rack, that reduced the amount of muck that attached to window. Not sure how badly one of those impacted the CX - but that was also before wipers became common on utes.

 

Low pressure area for sure maybe a dam or wing would help.

 

about adding some vortex generators to slightly alter the trailing edge aerodynamics of the roof....

 

Good idea Jet 1 I think I will give that a try, maybe some boundary layer energizers which have a low profile design, you would not see them as much.

 

my evo had vortex generators but still would mess up the trunk. maybe instead a rear diffuser would work.

 

bet they took stuff like that off the vehicle because of drag...loss of mpg's

 

properly applied, vortex generators would IMPROVE fuel efficiency at the cost of looks.

http://www.airtab.com/en/

 

agreed...but if you keep the flow onto the glass, then the idea is not to streamline but to disrupt the low pressure and keep the glass from accumulating snow/dust/etc. That won't be an aerodynamic feature because you would want the airflow to leave the top of the vehicle smoothly, not follow down the back to clear the back window. Just my thought on this, not nearly an expert...just an observation. But a scoop on top of the rear of the vehicle to direct airflow to the back glass would certainly be a hugh increase in drag from my viewpoint, even though I could be wrong.