How long can the weather forecast last?

A month. The longest forecast period of weather forecast can be determined according to different time scales, and the longest time range that weather forecast can provide is several weeks to one month. This long-term forecast is mainly based on meteorological models, taking into account the influence of convective atmospheric circulation, air pressure, temperature, humidity and wind direction. However, such a long-term forecast has certain uncertainty, because the change of weather system is very complicated and influenced by many factors, including topography, ocean, solar radiation and human activities. Therefore, with the extension of forecasting time, the accuracy of forecasting will gradually decrease.