Is there any factual basis for the impression that you lose heat much faster when it’s just above freezing (33F or 1C) and very damp and humid, compared to just below freezing when it’s dry? Does the relative humidity affect the heat conductivity of air?
All else being equal, I believe air becomes slightly less conductive (thermally speaking) as the RH increases.
"13. Does humidity or being near a large water body affect on windchill?
When we tested the new Windchill Temperature Index (WCTI), our researchers applied the new index to 12 test subjects. The results of the tests showed that relative humidity was an insignificant weather parameter, less than one degree at worst. To simplify the calculation, relative humidity was left out of the formula.
We did research a wet windchill or blowing water spray. This research was to simulate a person near a body of water or a mariner. These findings are being finalized and may be incorporated for the winter season 2003-2004."