Icing is a huge concern. On a drone it just adds weight but it can add up.
Don't fly through clouds.
Flying near waterfalls is where you could find freezing mist. That can accumulate very fast.
I know, FOR A FACT, that you can't hear drones 4-500 feet up.
I know most drugs are widely available in Portland but that doesn't mean you have to partake. Just sayin'