Comments: PAT *ʒ́ǝ-nǝ (cf. also Bzyb. á-ʒ́ǝn), with a usual temporal / locative suffix *-nǝ.
For phonetic reasons the PAT root should be kept apart from PWC *bž́V 'winter' (PAK *bžǝ-ħá > Ad. bžǝħa, Kab. bźǝħa; Ub. bž́a) (PAT *ʒ́ can not go back to *ž́ which is unmistakenly reconstructed on basis of other forms).