What indicates that a warm front might pass soon?

The appearance of ice pellets is an indicator that a warm front might pass soon because it typically signals the presence of a temperature inversion. As a warm front approaches, warm, moist air overrides cooler air at the surface, leading to the formation of various precipitation types. Ice pellets, or sleet, occur when snowflakes fall through a layer of warmer air and partially melt before refreezing as they pass through a layer of cold air closer to the ground. This phenomenon often occurs right before the warm front arrives, as the transition from snow to rain is taking place.

In contrast, clear skies and visibility would generally suggest stable weather conditions, not the imminent arrival of a warm front. High altitude clouds often form ahead of a warm front, but they are not a definitive sign that the warm front itself is about to arrive. Stable air layers indicate a lack of atmospheric disturbance, which is contrary to what you would expect when a warm front approaches. Thus, the presence of ice pellets serves as the most direct signal of changing weather conditions associated with an approaching warm front.