Notes to Dewpoint and Windchill:
Air can at a certain temperature only carry a certain amount of water
(water vapor), which also increases and decreases with temperature.
If the air temperature decreases below the dewpoint (saturation
point), the excessive water vapor will condense and fall out in form of
dew, fog or rain. At a temperature of e.g. 59° F and a relative humidity
of 50% the dewpoint will be about 41° F, at 80% humidity about
53.6° F. At a relative humidity of 100% saturation is reached, i.e. the
dewpoint is 59° F. At a dewpoint below freezing the fallout will become
frost or snow.

Windchill has been introduced for battle planning during World War II.
It represents not the real measured but the temperature a person
feels in open area under the influence of wind and cold. Windchill is
laid out in tables for various temperatures and wind speeds. At an
outdoor temperature of e.g. 46.4° F and calm winds a person moving
at a speed of 13 mph will already feel a windchill temperature of 32° F.