Not everyone in ancient Greece saw clouds as omens. Around 340 BC Aristotle wrote the Meteorologica, a long study of what happens in the sky and the air: rain, wind, hail, thunder, rainbows and the clouds that bring them. His explanations seem odd now. He believed the sun's heat drew moist and dry exhalations up from the earth and sea, and that clouds formed when the moist kind cooled and gathered.
The details were mostly wrong, yet the move was bold. Clouds became something to explain, with causes you could argue about, instead of something only a priest could interpret. The word meteorology still comes from his title, and means the study of things high up.
His pupil and successor Theophrastus is linked with a short work called On Weather Signs, a practical collection of what the sky tells farmers and sailors. Its entries are the ancestors of folk sayings still in use: how the sunrise looks, how clouds gather over hills, and what a certain haze might mean for tomorrow. Scholars debate how much of the book is Theophrastus himself, and how much was gathered by others.
Here is a second, quieter way of reading the sky. A weather sign does not carry a message from anyone. It is a pattern, noticed over many years, that points to what is coming. Divination and forecasting have been neighbours ever since, and the oldest sky-watchers probably did both on the same afternoon.
