SetterGuy, The only downside to rain is just brings some wind with it. If you do it before the rain that would be fine. If you do it after the rain and conditions are still very calm to achieve a good even application, even a slight overlapping application, their might be an advantage from another inch or 2 of water in the pond which will give more hydraulic pressure above the soilfloc to push it down into the cracks. It works best with the pond at full pool at maximum hydraulic pressure forcing the polymer to find the cracks. If the rain is a light rain it won't matter either way.
I had the ability to fill my pond to capacity using my well, I understand not everyone can do that
