A plane’s wings and a helicopter’s rotors are shaped such that the distance across the top of them is longer than the distance across the bottom of (front to back). The top is curved. This longer distance causes the air passing across the top of the wing/rotor to move faster than the air passing across the bottom as the wing/rotor gains speed. Faster moving air causes lower pressure, which in turn creates the ‘lift’ on the top of the wing/rotor. Same reason you hear a house could explode during a tornado due to the fast winds on the exterior, which create a much lower pressure than the air in the house. Therefore the old wise tale to open the windows so pressure can normalize. Or why you ears pop on a plane, etc. I’m not sure how icing impacts a wing versus a rotor. But considering drones are not flying at 30+ thousand feet where it is -40, probably not a problem for them. Doubt snow will impact them, and am not sure how rain could freeze on them at that level of the atmosphere if it isn’t already frozen (snow/freezing rain).