What must be included in a weather report when ice crystals (IC) are present?

When ice crystals (IC) are observed, it is essential to indicate cloud cover in the weather report. Cloud cover provides vital information about the type and extent of clouds present, which is crucial for understanding the overall weather conditions, especially when ice crystals are involved. Ice crystals typically form in colder parts of a cloud, often in clouds that are composed of supercooled water droplets.

By reporting cloud cover, meteorologists can assess the potential for icing conditions, visibility issues, and the overall stability of the atmosphere. This information supports pilots, air traffic control, and meteorologists in making informed decisions regarding flight safety and weather forecasting.

The other options, while they may relate to various weather phenomena, are not specifically required when ice crystals are present. Visibility being less than one mile is not a condition that directly relates to the presence of ice crystals, nor is the presence of thunderstorms or the location of other weather phenomena strictly necessary to mention in the context of ice crystals. Thus, the reporting of cloud cover is the most relevant and crucial component in these scenarios.