What is a key indicator of a warm front in terms of cloud formation?

A warm front is characterized by the gradual uplift of warm, moist air over cooler, denser air. As this warm air rises, it cools and condenses, leading to the formation of clouds. The presence of stratus clouds is a common indicator of a warm front, as these clouds are typically formed in stable atmospheric conditions when warm air overrides cooler air. Stratus clouds often appear as uniform, gray layers, bringing steady precipitation before and during the frontal passage.

In contrast, cumulonimbus clouds are typically associated with cold fronts, where rising air leads to strong upward motion and convective activity. The formation of only cirrus clouds indicates a high, thin cloud type usually found in the early stages of weather changes, but does not adequately represent the cloud development typical of warm fronts. Lastly, saying that a warm front brings no cloud formation is inaccurate, as the defining characteristic of a warm front is indeed the development of various cloud types, particularly stratus. Thus, option B correctly identifies stratus clouds as a key indicator of a warm front.