What are the criteria for classifying weather?

The daytime mentioned in the weather forecast refers to the period from 8:00 to 20:00 local standard time, of which 17:00 to 20:00 is called evening; after 20:00 to 8:00 the next day is called night. Sunny refers to the sky condition when the cloud cover in the sky is less than 30% (i.e. 30%) throughout the day; cloudy refers to the sky condition when there are 40-70% of medium and low clouds or 60-100% of high clouds in the sky; less Cloud refers to the sky condition when there are 10% to 30% of medium and low clouds or 40% to 50% of high clouds; overcast means that the sky is dark and densely covered with clouds, or the sky still feels dark even though there are gaps in clouds (the total cloud amount is 8 (above), and occasionally weak sunlight can be seen through the gaps in the clouds.
Light snow: The daily snowfall (melted into water) is less than 2.5 mm. Moderate snow: Daily snowfall (melted into water) 2.6-4.9 mm. Heavy snow: The amount of snow falling during the day (which melts into water) reaches or exceeds 5.0 mm.

Sunny (or few clouds): refers to cloudless, clear blue sky, or only a few clouds , the cloud cover is less than 30%.
Cloudy: means that the clouds cover most of the sky, the total cloud cover is greater than 30% but less than 70%, and the sun can penetrate the clouds to the ground.
Cloudy: the clouds are almost covered In the sky, the total cloud cover is greater than 70%.

Grade classification standards are:
Light rain: rainfall less than 10mm in 1d (or 24h).
Moderate rain: 10-25mm rainfall in 1 day (or 24 hours).
Heavy rain: 25 to 50mm of rainfall in 1 day (or 24 hours).
Heavy rain: 50 to 100mm of rainfall in 1 day (or 24 hours).
Heavy rainstorm: 100-250mm rainfall in 1 day (or 24 hours).
Extremely heavy rain: rainfall exceeding 250mm in 1 day (or 24 hours).
Light snow: A snowfall process in which the amount of snowfall within 12 hours is less than 1.0mm (equivalent to the amount of melted rainwater, the same below) or the amount of snowfall within 24 hours is less than 2.5mm.
Medium snow: a snowfall process in which the snowfall amount is 1.0~3.0mm within 12 hours, or the snowfall amount is 2.5~5.0mm within 24 hours, or the snow depth reaches 3CM.
Heavy snow: a snowfall process in which the snowfall amount is 3.0~6.0mm within 12 hours, or the snowfall amount is 5.0~10.0mm within 24 hours, or the snow depth reaches 5CM.
Blizzard: A snowfall process in which the snowfall amount is greater than 6.0mm within 12 hours, or the snowfall amount is greater than 10.0mm within 24 hours, or the snow depth reaches 8CM.
Heavy blizzard: a snowfall process in which the snowfall amount is greater than 12.0mm within 12 hours or the snowfall amount is greater than 20.0mm within 24 hours or the snow depth reaches 16CM.
Extremely heavy snowfall: a snowfall process in which the snowfall amount is greater than 24.0mm within 12 hours, or the snowfall amount is greater than 30.0mm within 24 hours, or the snow depth reaches 32CM.
The classification standards for rainfall levels will consider the following factors:
1. Rainfall amount: Depending on different regions and different purposes, the classification standards for rainfall levels may be different. Generally speaking, rainfall can be divided into light rain, moderate rain, heavy rain and heavy rain. Specific classification standards can be determined based on historical rainfall data and actual conditions.
2. Rainfall duration: In addition to rainfall amount, rainfall duration is also an important consideration in classifying rainfall levels. For example, long periods of light rain may cause flooding, while short periods of heavy rain may cause flash floods.
3. Geographical environment: Under different geographical environments, the classification standards for rainfall levels will also be different. For example, mountainous areas may have a higher tolerance for heavy rainfall, while plain areas may have a greater impact from the same amount of rainfall.
4. Degree of impact: The classification of rainfall levels also needs to consider the degree of impact of rainfall on human activities and the natural environment. For example, rainfall has different impacts on agriculture, transportation, urban drainage systems, etc., so the classification standards need to compre hensively consider these factors.
The influencing factors and application scope of rainfall grade classification are an important topic involving the fields of meteorology and water resources management. Factors that affect the classification of rainfall levels include rainfall amount, rainfall frequency, rainfall duration, rainfall intensity, etc. Compre hensive assessment of these factors can help understand rainfall characteristics and trends, and provide scientific basis for water resources planning, irrigation decisions, flood pre vention and disaster reduction, etc. In addition, rainfall grade classification has a wide range of applications, covering agriculture, urban planning, ecological environment protection and other fields. Through the classification and analysis of rainfall levels, the impact of rainfall on different areas can be better understood, so that corresponding measures can be taken to cope with and adapt to the challenges of climate change and water resources management.
In summary: The influencing factors and application scope of rainfall grade classification are an important topic involving the fields of meteorology and water resources management.
[Legal basis]:
"Interim Measures for the Management of Issuing Weather Forecasts"
Article 3
The state implements a unified issuance system for publicly released weather forecasts and severe weather warnings. Meteorological stations at all levels under the jurisdiction of the National Meteorological Administration are responsible for publishing. The Central Meteorological Observatory and meteorological stations at all levels below are responsible for issuing weather forecasts and disastrous weather warnings within the station's area of ​​responsibility. The Central Meteorological Observatory and coastal meteorological stations at all levels are also responsible for issuing weather forecasts within their responsible sea areas. and severe weather warnings.

1. Definition of rainfall: Rainfall refers to rain, snow, hail, etc. that fall from the atmosphere to the ground as well as water vapor condensed into The total amount of water such as dew and frost, its unit is millimeters (mm).
2. The concept of rainfall intensity: Rainfall intensity refers to the rainfall amount within a unit period, usually calculated in millimeters/minute or millimeters/hour.
3. Standards of my country’s Meteorological Department: my country’s Meteorological Department usually divides rainfall intensity into the following categories: light rain, moderate rain, heavy rain, and heavy rain. The specific classification criteria are: light rain means the rainfall is less than 5 mm in 12 hours, or the rainfall is less than 10 mm in 24 hours; moderate rain means the rainfall is between 5 mm and 14.9 mm in 12 hours, or the rainfall is between 10 mm and 24.9 mm in 24 hours. mm; heavy rain refers to the rainfall between 15 mm and 29.9 mm within 12 hours, or the rainfall between 25 mm and 49.9 mm within 24 hours.
4. Classification of heavy rain warnings: The quantitative standards for heavy rain may differ in different regions, depending on local conditions. Meteorologically, heavy rains are usually divided into three levels: heavy rain means that the rainfall in 12 hours is equal to or greater than 30 mm, or the rainfall in 24 hours is equal to or greater than 50 mm; heavy rainstorm means that the rainfall in 12 hours is equal to or greater than 70 mm, or the rainfall in 24 hours is equal to or greater than 70 mm, or the rainfall in 24 hours is equal to or greater than 70 mm Equal to or greater than 100 mm; extremely heavy rainstorm refers to a 12-hour rainfall equal to or greater than 140 mm, or a 24-hour rainfall equal to or greater than 250 mm.