The weather forecast is 5 1. What does F mean?

Is to pay close attention to temporary changes in the weather. For example, it is predicted that the day after tomorrow will be a level 3 wind. After all, it is a prediction, and the accuracy rate cannot be 100%. Generally speaking, small changes in forecast time are rarely corrected, while fact reports are always followed up. If it deviates from the forecast, it will be announced to the public immediately. When things are serious, we will pay close attention to real-time reports.