Wow, I had no idea that driving into a severe wind would have such an impact on MPG.

My wife took the HCH down to southern CA into a 25-30mph (or more) headwind, completely exposed (in a valley with no trees), with no other traffic. MPG went from a normal of about 48MPG down to 38MPG! Going 65mph, even.

Further down towards LA, driving along the coast, with the wind at 10-15mph headwind, she got 47MPG.

Maybe I should have realized the effect of the wind -- I once drove our Mercury Villager minivan from Phoenix to LA into a huge headwind, and I could almost see the fuel needle moving from Full down to Empty. I got about 1/2 to 2/3 normal mileage on that trip.

Yeah, I've noticed that myself in my 04 Prius. It's been pretty windy around here for over a week. Couple that with the cold, snow, sleet and rain, and my MPG is suffering. I've only gone down a few MPG from about 48 to 46, but I still can't wait for better weather.

At 65mph, something like 80% of your total drag is aero drag. Wind is directly proportionate to it's speed, so if you're doing 65mph into a 25mph headwind, you have to overcome the drag equal to doing 90mph. About the only thing you have going for you better than if you really were going 90mph is that you still only have the internal engine friction losses, drivetrain, and rolling resistance associated with 65mph. Likewise, if you'd had a 25mph tailwind, you probably could have seen your mileage go up to 70-75mpg or so.