Enlil has all the characteristics of a weather god. Weather gods are typically unpredictable and often have irascible tempers; their favourite home is invariably a mountain. Enlil's epithets are kur.gal, 'great mountain', and lugal.a.ma.ru, 'king of the storm'. His temple ... was called the e.kur, 'the house (is a) mountain'. All the extant versions of the flood story credit Enlil with control over 'the sluice gates of heaven' that drown the earth. ... In the Mesopotamian context, where agricultural production was independent of rainfall, the positive and fertilizing powers of weather gods were not so strongly stressed as in their traditional homelands, such as Syria and Anatolia. Accordingly, Enlil was feared and respected rather than loved, since his force was felt primarily in sudden floods, raging storms and, even more threateningly, the shifting of water courses. Leick 2001, p 152-3
Enlil began as a Syro-Anatolian weather god, and developed into a pan-Mesopotamian deity with utter supremacy.
This is told in several narratives, including Enlil and Ninlil, and Enlil and Sud. There are three atmospheric deities: An (heaven, above), Enki (earth, below) and Enlil (the space between heaven and earth). Modern scholars have presumed Enlil to be associated with air, but air did not have a cosmic identity in Mesopotamia. This assumption has been drawn from later Babylonian theology, namely the Enuma Elish, where Marduk assigns the main gods different domains: Ea, apsu; Anu, heaven; and Enlil, the space between Anu's celestial abode and Marduk's temple at Babylon.
At Nippur, a city associated with arbitration, this came to be under Enlil's domain as well.
In most popular reference works about Mesopotamian deities, his name is taken to be Sumerian, composed of the title en and the component lil, 'wind ghost', and hence translated as 'Lord Air'. ... In recent years the etymology of Enlil has been re-examined and it is now thought that the name is the Sumerian rendering of an originally Semitic word, the very word for 'god', 'il, the root form of such well-known Semitic divine appellatives as El and of, course, Allah. ... Enlil not only has an apparently Semitic name, he was also always associated with the word kur, which signifies both the physical realm 'mountain' and the cultural term 'foreign'. Leick 2001, p 151-2
Enlil at Nippur
At Nippur, Enlil overtook Shamash's usual domian and had the strongest and most institutional association with justice and divine decision. The traditional place for debating problematic legal decisions was in the courtyard of Enlil's temple, the Ekur. This was fitting as Enlil's cult was based at Nippur, a city renowned for its political neutrality and a place where arbitration could be conducted.
Enlil and Ninlil
Enlil impregnates the nubile Ninlil in the marshes, ignoring her protests that she is too young and that he will get punished. It is emphasized that this occurs in Nippur, a city that was regarded for its learning, justice and morality. Enlil's case is debated in the courtyard of the Ekur, his temple at Nippur, and he is expelled from the city. Ninlil follows him, and they trick each other into mating three more times, begetting three underworld gods. Enlil's licentious behavior would have him banished from Nippur were it not or Ninlil's actions that teach Enlil the rules of civilized life. Thus he is eventually allowed into Nippur. Ninlil is praised in the concluding lines of the poem for acculturating Enlil, bringing him into Nippur's pantheon.
Enlil and Sud
This story follows a popular Sumerian theme where a non-urban male marries a city girl. This occurred with Inanna and Dumuzi, who thrills Inanna with his rough, tough personality; and in the Marriage of Martu, where Numushuda's unnamed daughter accepts the proposal of the wild, uncivilized Martu -- "described with outright urban prejudice as belonging to people 'who eat raw meat, have no house and will have no decent burial'" (Leick 2001, p 154).
Enlil falls in love with Sud, but rather than letting lust take over, he politely inquires about her parents and then goes through formal premarital motions: a proposal; delivery of bridal gifts; the wedding. This traditional Mesopotamian wedding is proclaimed a victory of culture. The hymn's final lines praise Sud's mother Nisaba, the goddess of grain and writing: thus, nature and culture were united. While Ninlil taught an amoral Enlil the rules of civilized life, making him suitable for worship at Nippur, in the tale of Enlil and Sud, he marries a local girl the proper way and thus follows another traditional, albeit less exciting, path to acceptance.
Maybe Leick 2001, p 151-154