Which weather phenomenon can create dangerous icing conditions for aircraft?

Supercooled liquid water droplets present a significant danger for aircraft because they remain in a liquid state even at temperatures below freezing. When these droplets come into contact with an aircraft's surfaces, such as the wings, propellers, or engine inlets, they can freeze almost instantaneously, leading to ice accumulation. This icing can drastically affect the aircraft's aerodynamics, increase weight, and impede engine performance, making it more difficult to control and increasing the risk of accidents.

Other weather phenomena listed, while they may pose risks or challenges, do not directly contribute to the same immediate threat of icing. Snowfall involves frozen precipitation that may not pose the same hazards as supercooled droplets, and while heavy rain showers can create other hazards like hydroplaning, they do not create icing conditions. Cloud formation can provide conditions for icing, but it is the presence of supercooled liquid water droplets within those clouds that actually causes the ice to form on the aircraft. Therefore, the correct answer underscores the unique dangers associated with supercooled liquid water droplets in relation to icing.