It's just a idiom. I've met, and I've met counterexamples.

People tend to pay attention to phenomena that are consistent with idioms. Or what you expect to see.

"On August 15th, Yun Zheyue, it snows and lights on the 15th day of the first month" reflects the echo relationship between holiday weather.

Mid-Autumn Festival is a traditional folk festival in China. As the saying goes, the Mid-Autumn Festival is especially bright. On the night of Mid-Autumn Festival, the bright moon is in the sky, and the silver light shines on the earth. In this pleasant and quiet night, people gather together to watch the bright moon and tell the children the story of the Goddess Chang'e flying to the moon, osmanthus tree and Jade Rabbit.

If the dark clouds cover the moon and the sky is gloomy, it is disappointing! But it means that another traditional festival in China, Lantern Festival, is full of snow and exciting when every household is decorating.

The echo relationship between the weather of these two traditional festivals has long been concerned by people. Over time, in many places, if there are dark clouds all over the sky on the night of August 15th, the phenomenon of snowflakes fluttering often appears on the 15th day of the first month. So people summed up the weather proverb: "On August 15th, Yun Zheyue, on the fifteenth day of the first month, the snow lights up", which was widely handed down.

Of course, the rhythmic activity of the atmosphere is a very complicated problem, and its causes, conditions, manifestations and many other aspects have not been clearly understood, and this regularity can not be matched in every place and year.

At present, many meteorologists are deeply studying the rhythmic activity of the atmosphere and its causes, and the research results in this area are undoubtedly of great benefit to the development of long-term weather forecasting.

On the surface, "Yun Zheyue" and "Snow Lights" are the echo phenomena of clouds and snow, but in essence they are the echo relations of two cold air activities. That is to say, if there are cold air activities around the Mid-Autumn Festival, the phenomenon of "Yun Zheyue" is caused. Then, before and after the Lantern Festival, cold air will invade again, forming a situation of "snow hits the lights". Therefore, the proverb "On August 15th, Yun Zheyue, it snows and lights on the 15th of the first month" is a reflection of the rhythmic activity of the cold air invading China for about five months. According to this proverb, many meteorological stations have studied the rhythmic relationship of cold air activity for about five months, and applied it to long-term weather forecast, and achieved good results; The weather on other days also has this rhythmic relationship, but it has not been generally noticed by people.

The echo relationship between holiday weather is a manifestation of atmospheric rhythmic activities.

Why is there a relationship between two holiday weather days apart from 150 days? It turns out that this is a manifestation of atmospheric rhythmic activity. The atmosphere of the earth is like a large band, with wind, clouds, rain, snow, thunder, electricity, fog and frost, as if the band played a movement with rich timbre. Many studies have shown that this large-scale movement played by the atmosphere also shows a certain sense of rhythm under the combined action of various physical factors.

That is to say, a certain weather process is obvious at a certain moment, and it becomes obvious again after a certain period of time under certain conditions, or it is manifested in other forms due to different seasons, just like the beat in music. On the surface, there is no direct evolutionary relationship between them, but in fact there is a certain connection. In climatology, the internal connection existing in this atmosphere is called the rhythmic activity of the atmosphere.