Source : Webster's Revised Unabridged Dictionary (1913)

Mildness \Mild"ness\, n.
   The quality or state of being mild; as, mildness of temper;
   the mildness of the winter.

Source : WordNet®

mildness
     n 1: good weather with comfortable temperatures [syn: {clemency}]
     2: mercifulness as a consequence of being lenient or tolerant
        [syn: {lenience}, {leniency}, {lenity}]