What about sleet? Sleet is pretty much the snowy slushy mush that you find at the side of the roads after a snow storm.
SLEEET IS A DANGER FOR DRONES. The problem with sleet is it weighs the drones down and is just a point where it can mess with the electroncs but not roll of off.
Snow can transition into Sleet very quickly.
And the worse thing that can happen to your drone is when sleep turns into rain because out of nowhere your drone will be coated with freezing rain.