What phenomenon occurs when a warm air mass replaces a cold air mass?

• A. Cold Front
• B. Warm Front
• C. Occluded Front
• D. Stationary Front

Answer: (B)

When a warmer air mass moves into and replaces a cooler air mass, a warm front forms. The warm air, being lighter, gradually slides up and over the cooler air, creating a broad, gently sloping boundary rather than a sharp one. As the front passes, temperatures rise and the weather tends to show a gradual, sustained warming with widespread light to moderate precipitation that can last for hours. This precipitation and cloud cover build as the warm air is continually lifted over the cooler air, leading to layered clouds such as stratus and nimbostratus forming ahead of and along the front. This pattern contrasts with a cold front, where a cold air mass pushes in and lifts the warm air rapidly, often bringing heavier, more abrupt rainfalls. An occluded front occurs later when a cold front catches up to a warm front, lifting the warm air off the ground, while a stationary front stays in place with ongoing but relatively unchanged weather.