The correct answer is B) Steadily falling barometric pressure. The steadily falling barometric pressure is a characteristic of the weather preceding an approaching warm front. As the warm front approaches, the barometric pressure drops, signaling the approach of the warm, moist air mass associated with the front. The other options are incorrect because: A) Gusty winds are more characteristic of a cold front, not a warm front. C) Decreasing relative humidity typically occurs behind a warm front, not ahead of it. D) Clearing skies are more associated with the passage of a cold front, not a warm front.