Flights should be planned to avoid which types of forecast atmospheric conditions?

The correct choice highlights the significance of avoiding icing and thunderstorms during flight planning due to the severe impact these conditions can have on aircraft safety and performance.

Icing can lead to a range of serious issues, including loss of lift and increased drag, which can substantially affect an aircraft's ability to climb, maneuver, and maintain control. It primarily occurs in clouds and precipitation at temperatures below freezing, making it crucial for pilots to plan routes that avoid these conditions to ensure the aircraft's performance stays within safe limits.

Thunderstorms, on the other hand, are hazardous due to their potential for severe turbulence, lightning, hail, and gusting winds, all of which can drastically compromise flight safety. These conditions can develop rapidly and are often associated with other dangerous phenomena such as microbursts and wind shear, which can lead to difficult situations for pilots.

Understanding these elements is essential for effective flight planning, as it allows for the identification of safe flight paths and avoids areas that could pose risks to passenger safety and aircraft integrity.