Thunderstorms which generally produce the most intense hazard to aircraft are

Explanation

PHAK notes that a squall line, a non-frontal band of thunderstorms, often contains severe steady-state storms and presents the single most intense weather hazard to aircraft. Steady-state storms may be part of a squall line but the line as a whole is the most hazardous, and warm-front thunderstorms are often embedded but generally less violent.