There is another factor that plays into this. For livestock there are wind chill charts based on dry hair coat and wet hair coat.

For example, Cattle with a dry winter coat experience moderate cold stress at around 0-10 degrees F. With a wet hair coat, moderate cold stress occurs in the range of 32-45 degrees.

I do not know if there are such factors calculated for humans, but do know that if your clothes are wet, you should knock some more degrees off the chart. Of course, I guess this would depend on the clothes since some materials insulate better when wet than others.