In "The Shawshank Redemption", how did Andy know that it would rain and thunder the night he ran away?

When Andy went to the warden's office, it was already thundering, so he planned to run away that day. After all, Andy goes to the warden's office every day to help keep accounts. Use the thunder of the thunderstorm that night to cover up the sound of smashing the sewer, and use the smell of feces in the sewer and the scouring of the river to ensure that you can escape safely and not be chased by the prison. Everything is a conscious act that is carried out inadvertently!

This book has its own golden house Andy, a young banker. If his wife cg hadn't been killed, Andy would have been guilty and his future would be incalculable. Andy is a man with a wide range of hobbies. He likes geology and rocks, so he is proficient in geology. When writing on the wall carelessly, a stone fell off the wall, so Andy found the wall structure through the falling stone.

In this way, Andy knows that this wall can be dug. He persevered in digging a tunnel that others thought would take at least a hundred years to finish! Andy's study of geology is entirely possible to infer weather changes from the ground or some animals. At the same time, his knowledge of astronomy is quite insightful, so through some routine geological observations and weather changes, he can calculate that it must have rained that night, which is also well-founded. Sure enough, there is a golden house in the book. Study hard, you will always need it.

Andy Andy, as a banker, his thinking logic is very strong. He spent the whole tunnel for 20 years. He made it clear what he needed to do every day in the past 20 years, such as covering the hole with posters of beautiful women, scattering the soil from his trouser pockets on the square every day through walking, and hiding the shovel in a book like the shell used by the warden to change bags. ...

On the day he left, no one noticed that his leather shoes were clean and shiny black. It can be seen from all these details that Andy is full of hope for life. After the warden killed Andy's important witness, he thought Andy was dead and about to get out of prison, so he didn't have much thought to guard against Andy. Andy also showed stability and continued to launder money for the warden without any other complaints. It is in this stable state that Andy has a chance to escape.

Imagine that a person can live in prison 19 years. Who would have expected that it is still full of yearning for itself? Although the film does not specify the reason why Andy escaped from prison that night, we can also guess that the thunderstorm really helped Andy a lot, but this is only an auxiliary measure. He has been preparing this plan for more than ten years. How can such a fresh plan be ignored in some small details?