Atmospheric water vapour frozen into crystals (4)

I believe the answer is:

snow

(Other definitions for snow that I've seen before include "'See amid the winter's ... (Christmas carol)" , "feature of 27 [THE BIG FREEZE]" , "Precipitation in the form of ice crystals" , "Wintry weather" , "that may arrive around Christmas time" .)

I've seen this clue in the Sydney Morning Herald.

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