Li-Po's hardly handle adverse conditions very well. A fall as short as 2 feet can destroy them, and I'd assume it would respond similarly with weather conditions. However, as far as I know, (and I asked quite a few questions when I got mine) they can only catch fire when the cells are pierced in a situation like this. If it was somehow hit by a twig or something, it would have already caught fire, since it almost always happens within the first 15 minutes. Now, unless your plane is waterproof, I wouldn't count on it surviving, but really, if you're willing to sacrifice an expensive battery, why can't you hire someone to get it down? If it were me, I don't think I would even leave as long as it was up there.