Aeromancy

Aeromancy (from Greek aero, "air", and manteia, "divination") is divination conducted by interpreting atmospheric conditions.

Types
There are several types of divination that can be categorized under the term "aeromancy":

Austromancy, divination by observing the wind. Anemoscopy is austromancy in which the wind direction and intensity is interpreted, whereas nephomancy is divination by the interpretation of the movement of clouds.
Ceraunoscopy, divination by the interpretation of thunder and lightning.
Chaomancy, divination by aerial visions, is nearly synonymous with aeromancy, but most often refers to nephomancy or cometomancy, divination by the appearance of comet tails.
Meteormancy, divination by meteors and shooting stars.

Histor
Due to the historical interest people have had in weather, seeing it as a medium by which the gods express both joy and anger towards those who worship them, it is no surprise that aeromancy is one of the oldest forms of divination. The Etruscans, and Babylonians in particular have found the signs in the sky to be of great interest and practice forms of chaomancy and ceraunoscopy.

Gods associated with the practice of ceraunoscopy
Tinia, the Etruscan god of lightning
Adad, the Babylonian god of thunder, lightning, and prophesy
Amon, Egyptian god of wind, fertility, life, and secrets
Aditi, Hindu Goddess of the sky
Agni, Hindu God of the sun, lightning, and fire

Modern forms
Some forms of modern aeromancy have taken a more introspective turn than their historical counterparts. For instance, modern nephomancy is a receptive, almost meditative process, by which a person is said to be able to examine their unconscious. The nephomancer studies the clouds, whose formations are random and constantly changing. The images and symbols the diviner picks out from the chaos are believed to have some sort of significance to the diviner, so long as he applies his own personal interpretations to the symbols, rather than those written or spoken about by another.