Which is not a form of frozen precipitation?

The correct understanding is that freezing drizzle is, in fact, a form of frozen precipitation. It consists of supercooled liquid droplets that freeze on contact with cold surfaces. This makes it a part of the range of frozen precipitation types, which also includes other forms like sleet and ice pellets.

In contrast, ice crystals, snow grains, and hail are all categorized as frozen precipitation. Ice crystals, for example, form directly from water vapor in the atmosphere without passing through the liquid state. Snow grains are small, white, ice pellets that fall gently and are a form of solid precipitation. Hail, on the other hand, forms in strong thunderstorms where updrafts carry water droplets into extremely cold areas of the atmosphere, allowing them to freeze into larger pellets.

Understanding these distinctions is essential for accurately categorizing different types of precipitation, especially in aviation meteorology, where knowledge of weather conditions directly impacts flight safety.