下雪了！
Xià xuě le!
Snow fell!
了 marks new situation, natural excitement
外面下大雪了，地上白茫茫的。
Wài miàn xià dà xuě le, dì shàng bái máng máng de
Outside heavy snow, ground is white and boundless.
白茫茫 = expanse of white, poetic
鹅毛大雪纷纷飘落，整个世界都变白了！
É máo dà xuě fēn fēn piāo luò, zhěng gè shì jiè dōu biàn bái le!
Goose-feather snow floating down in flurries, the whole world has turned white!
鹅毛大雪 = goose-feather snow = heavy snow, classical poetic image
More Chinese (Mandarin) Weather Phrases