history
From Cen Shen's (岑参) Tang frontier poem 《白雪歌送武判官归京》 (Song of White Snow, Seeing Off Adjutant Wu Back to the Capital). Couplet: 忽如一夜春风来，千树万树梨花开 - 'All at once, as if a spring wind came overnight, on thousands of trees, myriads of trees, pear blossoms bloom.' The twist: this is not spring - Cen is describing a sudden heavy snowfall in the frozen Western Regions. The comparison is startlingly tender for a frontier poem.
usage
Used for any vast white expanse - snow scenery, rime on trees, sometimes pear orchards in real bloom. Tour copy, photography captions, and winter poetry invariably reach for this line.
