Any Prius owners notice the poor visibility when driving on highway during a moderate or heavy rain/snowfall. The shade of the windshield changes and the view is not as clear. It almost looks like it is fogged up, but it's not. Defroster and air conditioner vents are of little help. Road spray makes condition worse. No problem with street driving under similar conditions. Thanks.
The windshield? no. Here, the snow is fluffy enough that it blows over the car at highway speeds even in moderate snowfall. If the vents aren't helping, check to make sure that your cabin air filter is clean. It may be so clogged that air isn't flowing through it properly and you're not getting the windshield to defrost as designed. The cabin air filter is located in a white "drawer" behind the lower glovebox.
It's possible you have a stubborn oil film on the inside or outside of the glass. You can use an aggressive detergent to clean this off, but be careful not to get it on the paint without a lot of dilution (garden hose handy). On the inside use several large cloths (hand towels work best), one with the aggressive detergent, the rest with just water and one dry to clean up. You get "stuff" on the inside of the glass from "outgassing" of the plastic interior, smoking inside the car, etc. One of the reasons I leave Pearl's windows open a bit in the garage so that stuff vents outside the car.
I have the exact same problem with my new '12 Prius Two... no fog nor film on the inside, but droplets of spray on the front edge of the side windows and mirrors make it really hard to view the side mirrors when driving in the rain. Car is new and clean but the poor visibility is making it scary to drive in the rain. No improvement with Rain X on the mirrors... plan on trying it on the side windows next.
With the 2012 Pri, I have no problems in the rain. The windshield must have been treated with something (maybe like Rain X). I can't get it clean/streak-free yet, which causes a vision problem with glare with low sun angles in the afternoon. I haven't experienced any snow yet.
There is a device, controlled by a little black stalk on the right side of the steering wheel. When you pull the stalk down, bad things go away.
