Learn Spanish (Latin America): Hay chance de que llueva.

While a lo mejor is a special exception that takes the regular indicative tense, most other phrases expressing probability or doubt trigger the subjunctive. Since hay chance de que (there is a chance that) introduces uncertainty, it requires the subjunctive llueva instead of the indicative llueve.

Is chance actually a Spanish word?

Yes! It is a loanword from English that is extremely common in everyday Latin American Spanish. It is treated as a masculine noun (el chance) and is used just like "chance" or "opportunity" in English.

Why is there a de before que? Can I just say hay chance que?

You need the de. In Spanish, the noun chance links to other ideas using the preposition de (similar to "chance of" in English). When you connect it to a new clause with a conjugated verb, you combine de and que to make de que. Dropping the de here is a common mistake that native speakers sometimes make, but strictly speaking, it is incorrect.

I recognize the word for rain, but why does it have a "ue" in llueva?