What do you mean it's cloudy on the fifteenth day of the first month and it doesn't stop in February?

It means that the fifteenth day of the first month is cloudy, and it won't stop too much in the following February, which means continuous rainy weather.

This sentence is an agricultural proverb of China. This proverb reflects the observation and experience of farmers in China on weather changes. It can predict the next weather through such proverbs, so as to better arrange farming activities. In agricultural production, the change of weather has an important influence on the growth of crops, and farmers attach great importance to the weather forecast.