How did Zhuge Liang know that there would be an east wind?

In Battle of Red Cliffs, Sun Liu's headquarters decided to launch a fire attack on Cao Cao, but in the middle of winter, there was only a northwest wind, Cao Bing was across the river in the northwest, and the allied forces were in the southeast, and Cao Bing was in full swing. If the allies set it on fire, it would only hurt their own warships. At that time, it was really "everything was ready, except the east wind."

At this time, Kong Ming was willing to use the southeast gale on the third night for the use of the allied forces to solve the urgent need of the war and agreed on November 20. Zhou Yu set aside his troops to build an altar for him, waiting for the movement. On the appointed day, at midnight, the southeast wind was strong, and the allied forces attacked by the wind, burning Chibi and defeating Cao Bing.

When Kong Ming and Zhou Yugang sent troops, they told Liu Bei, "But if you look at the southeast wind, the light will return." And ordered Liu Bei to send Zhao Yun to sail at the appointed place on 1 1 20th.

Extended data:

According to Pei Songzhi's quotation of Wu Li in the Three Kingdoms, Sun Quan challenged Cao Cao Jun many times, but Cao Cao failed to persist. Sun Quan personally sailed in a canoe and entered Caoshui Village from ruxu. As soon as Cao Cao saw it, he knew that Sun Quan was coming. It was Sun Quan who wanted to see the battle in Cao Jun in person (see Wu Ye of our military department).

Ordered the troops to be ready, and the arrows and crossbows were not allowed to shoot indiscriminately. Sun Quan walked five or six miles before Cao Cao came back. When he left, he beat drums at Cao Jun. These were seen by Cao Cao and he sighed, "Born as Sun Zhongmou."

But this is not the case with Wei Lue. It says that Sun Quan took a big boat, not a canoe. Cao Cao also didn't say that crossbows can't shoot indiscriminately, but ordered archery. As a result, 10,000 arrows were fired at Sun Quan's ship, and the ship tilted to one side. Sun Quan ordered a U-turn, so that "10,000 arrows were fired in unison" and then returned safely.