Zhuge Liang can observe the sky and predict the weather. Why didn't he expect the heavy rain in the valley above?

Let's start with Zhuge Liang. According to historical records, Zhuge Liang is also a legend with outstanding achievements in politics, military affairs and literature. Besides, he is particularly proficient in observing the sky, and the allusion of borrowing arrows from grass boats is the best proof. Of course, some analysts say that borrowing arrows from grass boats is just a story made up by the author to emphasize that Zhuge Liang is particularly proficient in watching the sky, and it is a real event that it rains in the valley.

In the Battle of Shanggu, Zhuge Liang asked Wei Yan to lead Sima Yi into the valley, and then arranged for the army to ambush in the high place of Shanggu, throwing all the wood, stones and rockets into the valley, trying to burn Sima Yi and Wei Jun directly in it. As a result, just as Wei Jun was about to be swallowed up by the fire, it suddenly began to rain, and it was a downpour. The heavy rain put out the fire and gave Sima Yi a chance to escape. Although Zhuge Liang was sure that it would not rain this time, after the incident, Zhuge Liang suddenly realized the truth that "God disposes" and thought that Sima Yi's immortality was providence, which greatly dealt a blow to Zhuge Liang's spirit.

Why did Sima Yi's life-saving rain fall so timely? From a scientific point of view, if the battle of Shanggu is a fire attack, it will rain no matter which day Zhuge Liang chooses, because according to the analysis of professionals, the terrain of Shanggu is narrow at the top and wide at the bottom. Anyone who has studied geography will know that once a fire breaks out, a large amount of hot air will rise rapidly, and a large amount of hot air will liquefy when it meets the cold air above. So, to be precise, this rain has nothing to do with the astronomical phenomena, but a chemical reaction caused by hot air.