Steel broke in cold conditions (5)
I believe the answer is:
sleet
'in cold conditions' is the definition.
(type of icy rain seen in cold conditions)
'steel broke' is the wordplay.
'broke' indicates an anagram.
'steel' anagrammed gives 'SLEET'.
(Other definitions for sleet that I've seen before include "In foul weather" , "unpleasant weather" , "Partly melted falling snow or hail" , "Cold precipitation" , "Mixed rain and melting snow" .)