How did Yang Liulang use the weather to repel the Liao army?

In the Song Dynasty, Yang Liulang was ordered to lead troops to Bazhou to resist the invasion of Liao soldiers. It's very cold in late autumn and early winter. Liao coach decided to take advantage of Yang Liulang's precarious position and launch an attack.

Yang Liulang ordered the soldiers to sleep during the day and fetch water in shifts at night. For three days and nights.

On the day of the decisive battle, the Liao army came to the city gate and saw an ice wall several feet high.

The commander-in-chief of Liao army ordered his men to attack the city by force. But as soon as Liao soldiers approached the ice wall, they slipped and went belly-up. Song Jun was in the city earlier and earlier, and the arrows shot at the Liao army like locusts. The Liao army was caught off guard and fled in a hurry.