Which weather condition is considered the most hazardous for icing?

Freezing rain and freezing drizzle are hazardous weather conditions for icing because they involve supercooled liquid water droplets that remain liquid at temperatures below freezing. When these droplets come into contact with aircraft surfaces, they freeze almost instantly, creating a significant layer of ice. This type of icing is especially dangerous since it can accumulate quickly on critical surfaces like wings, propellers, and tail surfaces, severely affecting an aircraft's performance and handling.

In contrast, heavy snow primarily consists of ice crystals that do not typically adhere to surfaces in the same way that freezing rain does. Rain showers might lead to some transient icing conditions, but they do not present the same risk as freezing rain, which can lead to rapid and substantial ice build-up. Similarly, cloudy weather without precipitation does not pose a threat of icing because there is no moisture to freeze. Therefore, freezing rain and drizzle are recognized as the most hazardous for icing due to their ability to produce severe, quick accumulation of ice on aircraft surfaces.