During the Winter months your may notice that your wWatts (weather watts) are higher than those you have been seen in the Summer. The main reason for this is Air Density. Colder temperatures bring us higher Air Densities, which means greater air resistance.
Air Density is the mass of air in the atmosphere measured in kg/m^3. As the mass of air increases so does the resistance we experience when traveling through it. Here’s an interesting video demonstrating the affects of temperature on Air Density.
Why does this affect wWatts?
We anchor the wWatts metric to an average air density. So as above average Air Densities are experienced when it is cold in the Winter the resistance and therefore Watts required to achieve the same speed.
Low Air Density also explains why PBs are often achieved on warm humid days at the Summer.