"It's snowing outside" 是表示"外面在下雪"的常用英文表达。
来源：这句话是由两个独立的词组组成的，"it's" 是 "it is" 的缩写形式，表示"是"的意思，"snowing" 是 "snow" 的动名词形式，表示 "下雪" 的意思。
例句:
It's snowing outside, better wear a coat before you go out.
(外面在下雪，出门前最好穿上外套。)
Look at the window, it's snowing heavily.
(看看窗外，正在大雪中。)
I can't bepeve it's snowing in May!
(我简直不敢相信五月里竟然下雪！)