要下雨了。

You use this when you see physical signs of rain. Maybe the wind picks up suddenly. Or perhaps the sky turns a moody charcoal grey. You can say it as a standalone sentence. You can also add it to a warning. For example, 快走吧，要下雨了 (Let's go quickly, it's going to rain). It is one of the most useful weather phrases you will ever learn.

Use it whenever you are outdoors or near a window. It works perfectly when you are hiking with friends. It is great for small talk with a neighbor. You can even text it to someone to warn them. If you are at a cafe and see people running, say it! It makes you sound observant and helpful. It is a very natural way to start a conversation.

Don't use this if it is already pouring outside. If you are soaking wet, use 下雨了 instead. The 要 implies the future, even if that future is two seconds away. Also, avoid using it in a very formal scientific report. Meteorologists might use more technical terms for precipitation. For your daily life, though, it is almost always appropriate. Just don't say it in a desert unless you're really sure!

In China, talking about the weather is a safe social lubricant. It is a polite way to show concern for others. Telling someone 要下雨了 often implies 'take care' or 'don't get wet.' It reflects a culture that values looking out for one another. In older times, this phrase was vital for farmers. Today, it's just vital for anyone wearing suede shoes. It is a universal human experience expressed simply.

You might hear 快要下雨了 which means 'it is just about to rain.' The 快 adds a sense of urgency. Another version is 好像要下雨了 (It looks like it's going to rain). This adds a bit of uncertainty if you aren't 100% sure. You can also say 天要下雨了 (The sky is going to rain). All of these are friendly and common. They show you are paying attention to the world around you.