What is the primary hazard of flying through a thunderstorm?

Flying through a thunderstorm presents multiple hazards, but turbulence and possible hail are particularly significant dangers associated with these phenomena. Thunderstorms are characterized by severe updrafts and downdrafts, which generate intense turbulence. This can cause abrupt changes in altitude and can challenge the control of the aircraft, making flight through or near these conditions extremely risky.

Moreover, hail is often produced within thunderstorms, especially in those that are strong or severe. Hailstones can vary greatly in size and can inflict substantial damage on an aircraft's structure, including the windshield and leading edges of wings. Therefore, the combination of severe turbulence and the potential for encountering hail makes this choice very relevant to the primary hazards during flight in thunderstorm conditions.

While strong winds, low visibility, rain, and electrical activity are also aspects associated with thunderstorms, they are typically secondary when considering the immediate and rapid hazards a pilot would face while flying directly through a thunderstorm. The combination of turbulence and hail poses a direct and significant threat to safety, making this the most pertinent choice in the context of this question.