clear moon, frost soon

used to refer to the traditional belief that a clear moonlit sky is often associated with the prediction of frost or cold weather in the near future

The origin of the proverb "clear moon, frost soon" is rooted in traditional weather lore, dating back to at least the 18th century. It suggests that when the moon is bright and clear in the sky, it is a sign that the weather will soon turn cold, as clear skies at night often lead to frost forming. This saying reflects an observation of nature's patterns, where a clear moonlit night often coincides with a drop in temperature. Today, the proverb is still used as a way to predict chilly weather, especially in the fall and winter months.