What is the primary weather hazard associated with flying in the winter?

The primary weather hazard associated with flying in the winter is the accumulation of ice and snow on aircraft surfaces. This phenomenon can significantly impact both the performance and safety of an aircraft. Ice and snow can affect the aerodynamic properties of wings and control surfaces, leading to reduced lift and increased drag. Moreover, ice accumulation can interfere with the proper functioning of instruments and controls, posing serious risks during takeoff, flight, and landing.

In winter conditions, temperatures can drop to levels where moisture in the air can freeze upon contact with the aircraft, creating ice on wings and other surfaces. This not only affects the aircraft's performance but can also complicate ground operations, requiring de-icing and anti-icing procedures prior to departure. Pilots must also be vigilant for conditions that could lead to frost formation, especially on critical surfaces.

Other options, while they may present challenges in specific conditions, do not represent the primary hazard faced in winter flying. High temperatures causing thermal turbulence is more of a concern during summer months, while dry air leading to engine failures isn't typical of winter conditions. Heavy rainfall is also not characteristic of winter weather, where precipitation is more commonly in the form of snow or ice rather than rain.