Cumulus clouds that grow taller through the afternoon often signal instability in the lower atmosphere. When their tops begin to flatten into an anvil, a thunderstorm is usually less than an hour away.
A halo around the sun or moon is caused by ice crystals in thin cirrostratus clouds. Old sailors read it as a sign of rain within a day, and they were right more often than not.
Morning dew forms when the ground cools below the dew point overnight. A clear, calm night with little wind gives the best chance of a heavy dew, and of fog in low valleys.
Coastal breezes reverse twice a day: the sea breeze blows inland in the afternoon as the land warms, and the land breeze returns at night as it cools faster than the water.