clear moon, frost soon

proverb If there aren't clouds in the sky at night, then a frost is more likely to happen in the early morning. A: "Wow, you can really see the moon tonight!" B: "You know what that means—clear moon, frost soon." I know you boys are having fun playing in the moonlight, but my flowers aren't going to be happy in the morning. Clear moon, frost soon. A: "Sky's clear tonight. Clear moon, frost soon." B: "Ugh, I'm sick of having to clean off my windshield in the morning!"