"Mare's tails and mackerel scales make tall ships take in their sails."
"Rainbow in the morning gives you fair warning."
When clouds increase, whole areas of stars may be hidden by clouds with groups of stars, still in the clear sky, seem to huddle together.
The halo around the sun or moon is a layer of cirrus clouds made of ice crystals.
Cicadas can't vibrate their wings when the humidity is very high, so may be silent when rain is approaching.