Is it taboo to have thunderstorms or rain on the Summer Solstice?

In folk traditions, especially among farmers, it is most feared to have thunderstorms or rainy weather on the Summer Solstice.
Proverb says: "If there is thunder on the Summer Solstice, there will be drought in June; if there is rain on the Summer Solstice, it will be hot during the Three Fu periods."
This is because both drought and heat can affect the harvest of crops for farmers who rely on the weather.
So, in ancient times, people hoped that there would be no thunder and no rain on the Summer Solstice.

Is rain on the Summer Solstice a bad omen?

The custom of "avoiding rain" on the Summer Solstice is essentially a kind of expectation for the climate. In ancient times, farmers divided the half month after the Summer Solstice into three periods: the first period (the first three days), the second period (the middle five days), and the last period (the last seven days). Farmers were most afraid of "rain during the period" and "thunderstorms and rain at the end of the period". Therefore, they had many taboos such as "being careful with daily life, avoiding curses, and refraining from shaving" (from "Qingjalu").
In the folk tradition, especially among farmers, it is most feared to have thunderstorms or rainy weather on the Summer Solstice. Proverb says: "If there is thunder on the Summer Solstice, there will be drought in June; if there is rain on the Summer Solstice, it will be hot during the Three Fu periods." For farmers who rely on the weather, both drought and heat can affect the harvest of crops. Therefore, in ancient times, people hoped that there would be no thunder and no rain on the Summer Solstice.
These customs reflect the helplessness of ancient farmers who relied on the weather. Because thunderstorms and rains within the half month after the Summer Solstice are mostly heavy rains, which are more harmful than beneficial to crop growth.
After the half month of the Summer Solstice, it is the peak of summer with scorching sun, and crops begin to need water. Therefore, farmers hope that the sky will provide timely rain. To this day, many rural areas in China still have such weather proverbs: "If there is a dragon at twenty minutes past, and rain at twenty-one minutes past, even the cracks in the stones will be full of rice."