Which weather phenomena is a condition to solicit PIREPs?

Thunderstorms are a significant weather phenomenon that can greatly affect aviation operations and safety. Pilots are encouraged to submit Pilot Reports (PIREPs) during thunderstorms because they provide critical information about conditions that may not be captured by radar or other ground-based weather observation systems. This includes details about turbulence, wind shear, lightning, and significant cloud formations associated with thunderstorms. These reports help other pilots and air traffic controllers make informed decisions regarding flight paths and safety measures.

The other options, such as clear skies, light winds, and stable air pressure, typically represent benign weather conditions that do not warrant PIREPs. Clear skies do not present any immediate hazards to flight, and light winds or stable pressure generally indicate a lack of severe weather that could impact travel. In contrast, thunderstorms can introduce a range of hazards that are essential for flight safety to report and disseminate.