A light intensity symbol (-) is never used to report which type of weather phenomenon?

The light intensity symbol (-) is specifically used in weather observation reports to indicate that a particular phenomenon is occurring at a light intensity. It's important to note that this symbol conveys information regarding the intensity of precipitation and is applicable in various contexts.

In the context of ice crystals, the use of this symbol is not appropriate because ice crystals, which are essentially tiny ice particles, often occur in very light concentrations that do not warrant a specific intensity measurement like rain or other forms of precipitation do. Ice crystals are usually observed as a type of atmospheric condition rather than a precipitation event that can be quantified with light intensity.

On the other hand, phenomena such as ice pellets, snow showers, and freezing drizzle can be reported with varying intensities, including light. These forms of precipitation can be more significant in their impact and can be measured in terms of how intense they are falling, thereby making the light intensity symbol applicable in those instances.