I think most cyclists are aware of how the air density in cold temperatures effects aerodynamics and in turn their speed for a given effort, but what I haven't seen is discussion of whether this causes the wind to have a multiplied effect on a rider. I've often felt that below 60 degrees F or thereabouts, a given wind speed becomes noticeably more difficult to ride into, independent of the diminished speed already caused by the increased air density. For example, when it's in the 30's, an 8-10 mph headwind seems to have the slowing effect of a 20 mph wind in the summer, but still has the normal effect of a 10 mph wind when at your back and your side.