Why is the weather forecast in Henan inaccurate?

As the name implies, the weather forecast is a kind of forecast and an estimate of the future weather, but there are many uncertain variables in the weather, which will change at any time, especially in areas with complex geographical environment, so the forecast will be biased (inaccurate). Even modern high technology can't achieve 100% accuracy, so the weather forecast can guide our work, but it is not necessarily the case. Don't people often say "something unexpected happens in the sky"?