Ok, so I live in Houston and commute about 1 1/2 hours to the west each morning. We just got another one of our cold snaps here, this one is a bit colder than we usually get. On a normal non windy day, I can get about 40 - 42 MPG on my communte to work. This week with the cold, and more importantly the stiff 20 - 25 MPH north wind, I have been getting 35 MPG. The temperature has been showing between 30 - 35 for the last few day, and the wind has been terrible. Now today the wind was just a very light breese, and the temp started at 30 at home and dropped to 28 by the time I got to work, but my FE to work was 38 MPG. This tells me that the temp has been playing a role in my poor FE, but the wind has been the biggest contributing factor. This is also with a cross wind, and not a head wind. Now, this is perfectly dry weather, and just cold, so if there was snow, ice or water on the road, I would be taking a bigger FE hit, but I bet the wind is what is causing most of the poor FE in the winter.

Is the wind stronger in the winter than in the summer in most places?

Does the wind stay constant from a given direction more in the winter and shift directions more in the summer?

BTW, all FE is from resetting my Nav's trip indicator at the start of each commute in the morning.

I have noticed wind to play a large roll in FE. I live at the beach and it is often windy.

Cold air is more dense than warm air. That means more drag especially at higher speeds. Here, drag is also further increased by the 1/16th inch encrusted road salt covering most of the vehicle. I'd wash it if it would make a difference for more than a day.

Two climate control systems, one inside and the other at the tailpipe.

2007 Camry Hybrid (in service June 2006)
FE: 6.67L/100km or 35.3 mpg (6.11L/100km or 38.5 mpg in summer)

Let's not forget the 500 lbs of snow and ice left on the car like I saw yesterday on the highway. A nice Prius covered with snow and ice travelling down the road without a care in the world with all that extra weight and air drag driving north into a 35mph headwind. And they wonder why the mpg is only 32. Then when the sun hits it in during the day and it starts to melt, hit the brakes and watch your windshield wipers get torn off their mounts by all the ice and snow cascading down the windshield from the roof. Some people just don't get it.