What does the rainfall of 20-40mm mean in the weather forecast?

Rain falls from the sky to the ground without evaporation, infiltration and loss. The depth of water layer accumulated on the water surface is called rainfall (in millimeters), which can directly indicate the amount of rainfall. Daily rainfall is the amount of rain per unit area (1 m2) within 24 hours of that day. At present, the commonly used instruments for measuring rainfall are rainfall cylinder and measuring cup. The diameter of the rain tube is generally 20 cm, and it is equipped with a funnel and a bottle. The measuring cup has a diameter of 4 cm and is used together with the rainfall tube. When measuring, pour the rainwater in the rainfall cylinder into the measuring cup, and you can know the rainfall of the day according to the scale on the cup.

According to the regulations of China Meteorological Bureau, the rainfall within 24 hours is called daily rainfall, and any daily rainfall below10mm is called light rain,10.0-24.9mm is moderate rain, 25.0-49.9mm is heavy rain, 50.0-99.9mm is rainstorm, and100.0-250.

A few areas have other provisions according to the specific conditions of this province. For example, in rainy Guangdong, if the daily rainfall exceeds 80 mm, it is called rainstorm; In Yan 'an, Shaanxi, where there is little rain, it is called rainstorm when the daily rainfall reaches more than 30 mm.

Don't worry if you don't have a rain cone at hand. You can make one by yourself with some commonly used utensils, and the effect is quite good. Take a disposable plastic or paper bowl with a diameter of 20 cm (you can choose a convenient paper bowl with a suitable size), cut a small hole slightly larger than corn kernels at the bottom, and then put the bowl on a pot without a cover. There is a glass bottle in the jar, and the bottle mouth is connected with the small hole in the bottom of the bowl. The simple rain tube is ready. After the simple rainfall pipe is completed, it can be placed 70 cm above the ground (the distance between the nozzle and the ground) to receive rainwater. After the rain stops, weigh the water in the bottle with a scale. 30 grams of water is equivalent to 1 mm of rainfall.