When a new air mass moves into an area, its characteristics can lead to different weather outcomes based on whether it's warmer or colder than the existing air mass.
If a warmer air mass moves into an area that has a colder air mass, the warmer air will rise. As the warm air rises, it cools and can condense to form clouds, potentially leading to precipitation such as rain. Therefore, the most likely occurrence would be:
The warmer air mass rises, and there will be clouds and rain.
This scenario is common in weather patterns where warm and cold fronts interact.