كُلُّ بِكْرٍ حُرَّةٍ
Every fresh cloud pouring rain unmingled with hail and harsh wind.
Bikr normally marks a first or pristine state; applied to a cloud, it evokes rain not yet exhausted. Ḥurrah indicates rain free of hail and rough wind in this commentary.
جَادَتْ عَلَيْهِ
It poured generously upon it.
Jādat belongs to the vocabulary of generosity. Using a human moral quality for rainfall gives the natural scene a gentle personifying effect.