This plot is described in the Romance of the Three Kingdoms, but it is not recorded in the official history. But despite the novelist's statement, this plot is not unreasonable: Zhuge Liang attacked Wei in the spring and February of Wei Qinglong's second year, which was a season when it was warm and cold. When Sima Yi was introduced into the valley, the Shu army ignited the gunpowder buried at the bottom of the valley, generating huge heat and rising accordingly. As we all know today, precipitation is caused by the intersection of warm and humid air currents. When the heat rising from the valley bottom above reacts violently with the strong cold air above, the sudden rainstorm is natural. Zhuge Liang is not a meteorologist. He knows the general meteorological laws clearly, but he can't predict this special sudden rainfall, so he can't be demanding-of course, Luo Guanzhong still doesn't understand the reason.