The weather forecast says it will be sunny, why is it still cloudy?

Cloudy can be sunny, cloudy is not sunny, sunny can be cloudy, sunny but not cloudy, sunny, sunny, cloudy, this is the truth

Cloudy means: the sky cloudiness becomes cloudy when the cloud amount is 2-8.
More clouds just means: the number of clouds you see occupies a large area of ​​the sky.
Sky conditions are determined by the amount of clouds in the sky and the intensity of sunlight
It is divided into four conditions: sunny, slightly cloudy, cloudy and cloudy
Sunny: the sky is cloudless, There may be medium and low cloud cover less than 10%, and high cloud cover less than 40%.
Share clouds: There are 10% to 30% of medium and low clouds in the sky, or 40% to 50% of high clouds.
Cloudy: There are 40% to 70% of medium and low clouds in the sky, or 60% to 100% of high clouds.
Cloudy: The sky is dark, densely covered with clouds, or there are slight cloud gaps, but it still feels dark.

Recently, many readers have expre ssed confusion about our frequent forecasts of cloudy days. After consulting the information, the difference between a sunny day and a cloudy day is often not very big intuitively. It is just a difference in the amount of cloud cover. On a sunny day, the cloudiness in the sky is less than 10%, with little cloudiness, the cloudiness in the sky accounts for 20-30%, and cloudy, when the cloudiness in the sky accounts for 40%-70%, and if the cloudiness accounts for more than 80%, it is considered cloudy. Judgment of how much cloud cover is in the sky often relies on the observation of experienced forecasters. There are very few cloudy days in the forecast, and the difference between cloudy weather and sunny days is very small. Many people originally thought that during the hot summer season, the clouds on cloudy days might absorb some ultraviolet rays, making the sunlight less dazzling. However, some studies say that the ultraviolet rays on the ground in cloudy days are stronger. Foreign researchers once conducted experiments to measure the light intensity values ​​on sunny days and cloudy days on an island. Experiments have found that the light intensity on a sunny day is 900 watts per square meter, while the light intensity value per square meter under cloudy conditions reaches 1,400 watts. Analyzing the reason, on cloudy days, there are clusters of altocumulus clouds in the sky that look like marshmallows. Although the sky is full, there are many holes. Altocumulus clouds are like reflectors, reflecting the sunlight from the upper layer, which is equivalent to double or even multiple times. Sunlight breaks through holes in the clouds. One consequence of this theory is that people in subtropical areas may be more susceptible to tanning than those in tropical areas. Because of the high cumulus clouds in subtropical areas in summer, it gives people the illusion that ultraviolet rays are not strong, so that they forget to take necessary sun protection measures such as applying sunscreen and using parasols, and are psychologically paralyzed by the sky. However, in summer in the tropics, there are many thunderclouds in the sky, which completely block the sunlight. Without reflection, there is nothing, and the ultraviolet rays are completely weakened. This conclusion reminds me of an example I experienced personally. When military training started when I was in college, there were white clouds in the sky every day. I told my classmates privately that such weather was great for military training. Unexpectedly, one summer passed, and all the students were as tanned as those from the equatorial region, only to realize that all the freshmen had been tricked by God.