Question

Is there any way to make rain go longer?

Answer 1

![enter image description here][1]

Damp Rock-
[1]: http://ts2.mm.bing.net/th?id=HN.608015185658777271&w=87&h=84&c=7&rs=1&pid=1.7
This rock thingy lengthens the duration of rain from 5 turns to 8 turns. It can be found on Route 14 and Route 19. I am pretty sure you can find it somewhere else too, but I don't really know.

Source: Bulbapedia

Comments

In the Connection Cave, after defeating hordes, you can get one.

Answer 2

In battle, if a Pokemon uses Rain Dance while holding a Damp Rock, it will extend Rain Dance for eight turns, instead of the usual five turns. Outside of battle, however, there is no such way. Sorry! D:

Hope I helped. :)
Source