Question

I cannot imagine a thunderstorm over a desert :D

Answer 1

You'd be surprised, actually. It's rare but it does happen, and deserts do get rain. In fact, thunderstorms don't always have rain and it's not the rain that makes it a thunderstorm anyway.

Thundurus is a roaming Pokemon so it should appear on any of the routes. Maybe it was Thundurus that caused the original sandstorms there?

Comments

Like the first part of your answer, this is unrelated to Pokemon. Examples of places that get thunderstorms without rain, or deserts/plains getting rain would be the Mid-West United states, many of the Plains that border the desert in Africa, places in Australia, and just most places along the leeward side of mountains, especially near oceans.

---

I know it is possible but...weird :D :D :D