I had already managed to finish that battle, and I was on the next battle where I have to gather apples, and it was slowing down there as well. That one doesn't appear to have weather effects, and I can't figure out what that map is called to check.
Not sure it's as bad as the previous battle with rain, but the slowdown is still significant.
EDIT: Found the map called "Out of Food"; don't see a weather effects line.