winter sky
Refers to the sky as it appears in winter, often with connotations of cold, clear, or overcast conditions typical of the season.
The stars look beautiful in the winter sky.
Today the winter sky is overcast and gloomy.
Compound of 冬 (ふゆ, 'winter') and 空 (そら, 'sky'), with rendaku voicing of そら to ぞら.