Which weather condition can significantly affect visibility while flying?

Thunderstorms can significantly affect visibility while flying for several reasons. Within a thunderstorm, there are intense rain showers, hail, strong winds, and turbulence, all of which can drastically reduce visibility. The heavy precipitation often associated with these storms can create a dense curtain of water that obscures the view, making it difficult for pilots to see the ground, other aircraft, or even navigation aids.

Additionally, thunderstorms can produce cloud-to-ground lightning and generate low-hanging clouds or fog due to the rapid changes in temperature and moisture levels, further degrading visibility. The associated turbulence and winds can also contribute to the difficulty of maintaining visual references, especially during takeoff and landing phases of flight.

In contrast, high humidity can contribute to haze or fog under certain conditions but does not have the immediate and severe impact on visibility that thunderstorms do. High altitudes tend to provide a clearer view above weather systems, while clear skies indicate excellent visibility conditions. Thus, the presence of thunderstorms poses a unique and significant threat to visibility in flight.