From Xu Hun's (
许浑) late-Tang poem 《
咸阳城东楼》 (East Tower of Xianyang City). The couplet reads:
溪云初起日沉阁,
山雨欲来风满楼 — 'Clouds rise over the stream as the sun sinks behind the pavilion; the mountain rain is about to come, and wind fills the tower.' Originally a pure landscape image; later became the go-to metaphor for political / organisational foreboding.