Some hazardous weather features:

1. Fog and Haze

Temperatures drop significantly in October. When the cold air encounters autumn rain, the abundant water vapor in the air soon reaches saturation, and then it turns into misty rain or fog after the rain. It is more prevalent in the night. When the humidity is high, there will be foggy regions formed in the southeast of Liaoning, the east of Hebing and Shandong, the south of Anhui, the west of Hunan, the west of Hubing, the basin of Sichuan, and Chongqing. Local transport and traffic safety is affected. On the morning of October 8, 2004, the first day of Cold Dew that year, a thick fog greeted the citizens going to work in Beijing. The visibility in some areas of Beijing was only 200 meters (thick fog is when horizontal visibility is between 200 to 500; dense fog is when horizontal visibility is between 50 to 200).

The atmospheric stratification is steady when it is controlled by high pressure. On windless days, tail gas, waste gas and dust are hard to diffuse, so haze forms easily. If humidity is high in the air, the weather with fog and haze at the same time will be formed.

2. Autumn rain in the West China

Autumn rain is a special weather in West China (including drainage area of Weishui River and Hanshui River, Sichuan, most areas of Guizhou, eastern areas of Yunnan, western Hunan and the west of Hubei). Precipitation is more than that of spring, less than summer, and concentrates in September and October. The intensity of the rainfall is not strong, but the rain lasts a long time. The total number of rainy days in September and October is generally 20 to 30. Particularly in the Sichuan Basin, autumn rain is very common in most years. These long-lasting rains and lessened sunshine take a heavy toll on this period of the harvest. In Cold Dew, the east area of South China sometimes suffers from the rain, which damages the harvest and sowing of crops.

3. Cold Dew wind

Cold Dew wind forms when the cold air of autumn invades the southern areas of China. It results in a temperature drop, shriveled grain rice and a reduction in farm production. Because this hazardous wind emerges in Cold Dew, it is named after it. Generally, the Meteorological Index of the damage to rice varies depending on the rice type and growth phrase, and the standards in different areas are not the same. In the middle and lower areas of the Changjiang River, the standard duration of Cold Dew wind is more than three days, with an average temperature lower than 20℃. In South China, the standard duration lasts more than three days and with an average temperature lower than 22℃.

4. Snow damage in plateau mountain areas

In late autumn, it begins snowing heavily at the junction of the Qinghai and Sichuan, western Sichuan and altitudinal plateau mountains, which has a major effect on local transportation and animal husbandry (The People's Republic of China Climate Atlas).

5. Tropical cyclone Although tropical cyclones

They are generally active from July to September, there are still tropical cyclones in October, though they are fewer in number. Some tropical cyclones in Hainan are still strong during this period.