、。
After dark clouds have gathered, a clear break comes.
Literal
Dark-clouds [subject-が] gathered-[resultative-ていた] after [at-に][topic-は], refreshingly clear-spell [to-に] become.
暗雲が立ちこめる 'dark clouds gather/hang heavy' — 暗雲 can be literal or metaphorical (figurative: 'ominous signs'). すっきりとした 'clear, refreshing.' The sentence works on both literal (weather) and metaphorical (things improve after dark times) levels.