Ṣahbāʾ here describes a reddish cloud; it would be mistaken to apply the word’s possible association with wine to every context. Jahām is a cloud depleted of rain, light enough to be driven rapidly; janūb is the south wind.
The cloud is not decorative scenery. Its light mass is hurried by the wind, providing a visible comparison for the she-camel’s hibāb when guided by the rein.