What characterizes a warm front?

A warm front is characterized by the gradual ascent of warm air over cooler air. This occurs when warm, moist air advances and rises, leading to increased humidity. As warm air rises, it cools, which can cause condensation and cloud formation. This process often results in conditions favorable for thunderstorms, particularly as the warm air meets the cooler, denser air.

The presence of high humidity and the potential for thunderstorms are defining features of warm fronts. Prior to the arrival of a warm front, one can expect increased cloudiness, followed by rain or thunderstorms as the front approaches.

The other options describe different meteorological phenomena. The description of fast-moving cold air replacing warm air reflects the characteristics of a cold front. The notion of cool air with no precipitation is more typical in stable atmospheric conditions, which are not associated with the dynamics of a warm front. Lastly, a sharp decrease in temperature would indicate the passage of a cold front rather than a warm front, where the temperature generally increases as the warm air moves in.