Final answer:
As the warm frontal system approaches, Cirrus clouds typically form initially, indicating changing weather patterns and the eventual arrival of precipitation as these clouds thicken into Nimbostratus clouds.
Step-by-step explanation:
As the warm frontal system approaches, the indicator clouds that initially form are typically Cirrus clouds. These clouds are high, thin, and wispy, appearing at the forefront of a warm front. As the front gets closer, these cirrus clouds often thicken and progressively lower in the atmosphere, leading to the development of clouds like altostratus and eventually Nimbostratus clouds, which can bring steady precipitation. Cirrus clouds don’t hold much moisture and don’t usually result in precipitation themselves, but their presence is a tangible sign that weather patterns are changing as the warm front nears. Cumulus clouds, on the other hand, are usually associated with fair weather or thunderstorms if they develop into cumulonimbus clouds, which is not typical for a warm front scenario.