This is also why, even when the outdoor thermometer reads negative-bajillion, but it's really sunny,† it still feels nice to take off your winter coat: the Sun

This is also why, even when the outdoor thermometer reads negative-bajillion, but it's really sunny,† it still feels nice to take off your winter coat: the Sun's radiant energy is heating your skin so you "are" warm regardless of the air temperature. † Very cold and very sunny generally go together: the air is too cold to hold moisture, so there are no clouds, so you get the sun.