Winter landscape feature melting down first? (9)
'winter landscape feature' is the definition.
'melting down first?' is the wordplay.
'melting' indicates an anagram.
'downfirst' with letters rearranged gives 'SNOWDRIFT'.
(Other definitions for snowdrift that I've seen before include "Wintry accumulation", "Wind-driven winter hazard", "Midwinter may show one", "Wintry feature", "Winter problem".)