People often distinguish sunny days, cloudy days and cloudy days according to the amount of what?

What we call sunny days, cloudy days and cloudy days are distinguished according to the amount of clouds in the sky.

In the meteorological industry standard, the percentage of cloud area in the sky is taken as the criterion: it is sunny when the cloud amount is 0% to 10%; 10% to 30% partly cloudy; 30% to 70% is cloudy; More than 70% is cloudy. It is not difficult to see that sunny days are not absolutely "cloudless in Wan Li". Partial cloudy is an essential item in observation, but it is not commonly used in forecast because it is close to sunny day.

Weather characteristics

Visually, when it is sunny or partially cloudy, the blue sky is like washing, and there is no cloud or only a small amount of cumulus in Wan Li; When it is cloudy, clouds cover most of the sky. Clouds are mostly cumulus clouds or layered clouds with a small range, and sunlight can shine through the clouds to the ground.

On cloudy days, a large range of layered clouds cover the sky, which has a great influence on the light transmittance, and generally the sun is not visible. Therefore, when it is cloudy, white clouds are generally floating in the blue sky; On cloudy days, there will be a sense of depression that "dark clouds are pressing the city to destroy".

In addition, "sunny to cloudy" in the weather forecast means that it will appear sunny first, and then gradually turn cloudy, with the emphasis on the process of weather change, that is to say, the weather will change; "Sunny and cloudy" means that it is sunny most of the time, with occasional clouds, and a few times the amount of clouds increases.

Cloudy to cloudy indicates the possibility of bad weather, and the cloud cover gradually exceeds 70%. The forecast of sunny, cloudy and cloudy days is mainly based on the consideration of weather system.