What does it mean that there is rain on the weather forecast line and there is no rain off the line?

The weather forecast said it would rain, but it didn't. Rain on the weather forecast line means it will rain on the weather forecast platform, and no rain off the line means it doesn't rain in reality, so it means it will rain on the weather forecast line but not on the weather forecast. Weather forecast (measurement) or meteorological forecast (measurement) is to use modern science and technology to predict the state of the earth's atmosphere in a certain place in the future.