I recently visited one of the Winterlude activities in Canada's capital region. There was virtually no wind, the air was dry, and the sun was shining. I felt so warm and I was perspiring so much that I had to take off my winter jacket. In this situation, I think there is an opposite of the "windchill factor" in action. What I call "sunwarm factor" made me feel that it was +5 C even though the temperature was -10 C and the windchill was -10 (unitless).
I also learned that Canada's windchill index does not take relative humidity or atmospheric pressure into account, unlike Australian Apparent Temperature whose formula comprises water vapour pressure. This omission explains why it feels so cold on a windless but humid day, like -15 C even though the actual temperature is only 0 C and the windchill is 0 (unitless).
Ideally, how cold or how hot one feels must be determined by mutually-exclusive independent parameters convoluted with personal profile such as one's perspiration rate, which varies widely among individuals.
