Why in the Romance of the Three Kingdoms, Zhuge Liang can calculate the east wind fog, but not the rain in the valley above?

In 208 AD, Cao Cao led a great army to crusade against Jingzhou. Due to the death of Liu Biao, Liu Cong, the new Jingzhou animal husbandry, was timid. He didn't dare to face Cao Cao's soldiers directly, so he went out of the city to surrender and Jingzhou fell. Liu Bei had to flee to the south, but was caught up by Cao Cao's army and almost died.

Just then, Lu Su appeared in Jingzhou to meet Liu Bei. Later, Liu Bei decided to unite with Sun Quan to resist Cao Cao. In order to complete the alliance, Zhuge Liang and Lu Su came to Jiangdong together. Prior to this, Zhuge Liang had made great contributions in the Battle of Bowangpo and the Battle of Xinye, and was gradually known to the world. After coming to Dongwu, Zhuge Liang once again won the admiration of Zhou Yu and others with his own strength.

At that time, Zhou Yu designed Jiang Gan, one of Cao Cao's men, to steal books, so that Cao Cao killed Cai Mao and Zhang Yun, who were good at practicing the navy, and got rid of his worries. But Zhou Yu saw that Zhuge Liang was a rare talent, but Zhuge Liang could not be used by Jiangdong, so he planned to design and get rid of Zhuge Liang.

To this end, Zhou Yu did not hesitate to make 100 thousand arrows in ten days as an excuse to go to war with Cao Cao. Zhuge Liang knew that Zhou Yu was deliberately targeting him, but he didn't panic. But told Zhou Yu that there could be 100 thousand arrows in three days. In order to persuade Zhou Yu, Zhuge Liang did not hesitate to make a written pledge to fulfill a military order, and if he failed to complete the task, he would go to hell to pay.

At that time, Zhuge Liang was sure of winning, mainly because he had calculated that there would be heavy fog in three days. At this time, the river was foggy, and Cao Cao was suspicious and did not dare to attack rashly. Under such circumstances, Zhuge Liang successfully borrowed the arrow of the straw boat and completed the task assigned by Zhou Yu.

After the straw boat borrowed an arrow, Zhuge Liang borrowed the east wind to help Zhou Yu complete the feat of burning Chibi. At that time, Sun and Liu Lianjun had successfully used Pang Tong to let Cao Cao pick up the warships on the river. At the same time, Zhou Yu and Huang Gai staged a bitter plan and successfully persuaded Cao Cao and Huang Gai to surrender to him. However, just as Zhou Yu was preparing to attack Cao Jun, he suddenly remembered that it was the middle of winter and there was no southeast wind on the river. Without the help of the east wind, the fire attack could not be realized.

But at this time Zhuge Liang said that he could try to borrow the east wind from the altar. He asked Zhou Yu to build a nine-foot-high seven-star altar for him, and then he did it himself. A few days later, as expected, the southeast wind blew. Seeing Zhuge Liang's ability, Zhou Yu felt that Zhuge Liang could not stay, so he sent someone to the Seven Star Altar to kill Zhuge Liang. But Zhuge Liang had long expected that Zhou Yu would have this skill, leaving the Seven Star Altar ahead of time and returning to his base area, Xiakou.

However, Zhuge Liang is not a fairy after all. Perhaps he was able to borrow the east wind because he correctly predicted that there would be an east wind at this time, just like the foggy weather that day, which led to the story of borrowing the east wind from the altar. But strangely, because Zhuge Liang knew astronomy above and geography below, his grasp of the weather was very accurate, comparable to the weather forecast of that era, so Zhuge Liang was not sure that it would rain in the upper valley during his northern expedition.

At that time, Sima Yi insisted on not fighting. Zhuge Liang designed to introduce Sima Yi into Shanggu and ignite it with flammable substances prepared in advance. Sima Yi was about to be burned to death in Shanggu, but at this time, it suddenly rained heavily and put out the fire. Sima Yi also escaped. Zhuge Liang, who is good at calculating the weather, did not calculate that it would rain in the valley above. Why?

You should know that Chibi is not far from Zhuge Liang's seclusion, so even in Jiangdong, Zhuge Liang can understand the local climate and environment. But Shanggu is not in Shuhan area or Jingzhou. Zhuge Liang is not familiar with this place, so naturally he can't fully grasp the local meteorological conditions. What's more, Zhuge Liang had too many things to deal with at that time and didn't have enough time to study, so he ignored the weather problem in his design, which would make Sima Yi escape.

The author thinks that Sima Yi didn't die in Shanggu after all, so when Luo Guanzhong wrote the Romance of the Three Kingdoms, he naturally wouldn't write Sima Yi here. So Zhuge Liang planned his life, but ignored the fact that it would rain here in Shanggu.