。
In the evening, a few clouds started to come out.
Literal
Evening [into-に] become-[and-て], a-few clouds [subject-が] came-out.
A simple weather/time-of-day observation. 夕方になって is a fixed temporal phrase: '(when) it became evening.' 雲が出る ('clouds come out / appear') is the natural Japanese idiom for clouds appearing, treating the sky as a stage. ~てきた marks the change arriving into the speaker's awareness — 'started to appear.' Polite past form for diary-like narration.