据说明天会下雨用英语怎么说

"It's supposed to rain tomorrow" 是表示明天会下雨的英文短语。

来源： "It's supposed to" 是“应该”的意思，而 "rain" 是“下雨”的意思。

例句：

I heard it's supposed to rain tomorrow, so I'll bring an umbrella. (我听说明天会下雨，所以我要带把伞。)
It's supposed to rain tomorrow, so we should cancel our picnic plans. (明天应该会下雨，所以我们应该取消野餐计划。)
I hope it doesn't rain tomorrow, but it's supposed to. (我希望明天不下雨，但是应该会下雨。)