Incorrect grammar

Question

Technically, you cannot use the near future for weather forecasting.  A forecast is a prediction; therefore, the future simple should be used.  The only grammatically correct way to use the near future for weather is when you are outside, the wind whips up, storm clouds roll in with thunder/lightening...then, you can say (in English, French, or Spanish) that it's "going to rain".  Perhaps in very colloquial language the near future is used for weather forecasts, but it is wrong, and this should be clearly noted in the lesson.

Accepted Answer

Hi Talk,
I see your logic but in practice, you can actually use both future tenses in predicting the weather forecast.
As you can see from this real-life weather forecast, a mixture of tenses are used,  the present, future, and near-future - 
https://meteofrance.com/previsions-meteo-france/ile-de-france/3
Bonne Continuation !

Answer

Completely agree with Cécile. Prescriptive grammar seems to be your guide, but others have descriptive grammar available.

https://amyrey.web.unc.edu/classes/ling-101-online/tutorials/understanding-prescriptive-vs-descriptive-grammar/