Which of the following is a sign of an approaching cold front?

Recognizing the signs of an approaching cold front is essential in aviation weather. A sharp temperature drop paired with an increase in wind speed indicates the imminent arrival of cooler, denser air that is pushing into an area. This shift occurs because as a cold front advances, it forces warm air upward, leading to changes in temperature and wind dynamics.

Typically, the onset of a cold front will bring a noticeable drop in temperature, as the cold air replaces the warm air currently in place. Additionally, as the cold front moves in, the winds often shift and increase in speed due to the pressure differences created between the air masses.

The other options do not reflect the characteristics associated with a cold front. Sustained high temperatures indicate a stable atmospheric condition, while a gradual rise in humidity suggests the presence of warmer air possibly preceding a warm front. Mild winds and clear skies are more indicative of fair weather conditions, which can be associated with high-pressure systems, not an approaching cold front. Thus, the sharp temperature drop and increase in wind speed are key indicators of a cold front's approach.