Riddle: There is a monster in the Jianghuai area. It comes when the plums turn yellow. It causes harm almost every year if it doesn't move around when it comes.

The full text is:

There is a monster in the Jianghuai area. It comes when the plums turn yellow.

It has come and refused to leave, causing harm almost every year.

Refers to the plum rain season

Every year from mid-June to early or mid-July, the middle and lower reaches of the Yangtze River in my country refer to the 28-34°N range east of Yichang, or Jianghuai watershed. A period of continuous rainy weather occurred in this narrow area in southern Japan. This is the season when plums are ripe in the south of the Yangtze River, so it is called "Meiyu". The main characteristics of Meiyu weather are cloudy and rainy weather, short sunshine, high relative humidity, abundant rainfall, and often heavy rainstorms.

Meiyu is a large-scale precipitation weather process, which is caused by the relatively stable atmospheric circulation. During the Meiyu period, blocking high pressure is often maintained in the higher latitudes north of 50° N, causing the cold air to be unable to Southward on a large scale, and in lower latitudes. The ridgeline of the western Pacific subtropical high is located around 20-25°N. The middle and lower reaches of the Yangtze River in my country are the intersection area between the southwest warm and moist air flow transported by the western Pacific subtropical high and the small cold air from the north. There are often shear lines in this area, southwest vortices are active, and quasi-stationary fronts and frontal cyclones are active on the ground. , causing long-term rainy weather and repeated heavy rain processes, a Meiyu front cloud belt is often stable on satellite cloud images.

However, the dates of "plum season" and "plum season" are different every year. The difference between morning and evening can be more than 40 days. Sometimes there will be "less plum blossoms" or "empty plum blossoms", and sometimes there will be "full plum blossoms" phenomenon. For example, in 1954 and 1991, the Meiyu period was particularly long and rainfall was extremely heavy, causing floods in the Yangtze and Huaihe River basins. In 1994, an abnormal drought occurred in Shaomei and Jianghuai areas. This abnormal situation during the Meiyu period is often associated with abnormal changes in global atmospheric circulation.