How do weather symbols represent sunny days?

1 1, 16, 17 is sunny, 12- 15 is sandstorm.

Symbols of weather phenomena specified in the ground meteorological observation specifications of China Meteorological Bureau;

Weather graphic symbols issued by China Meteorological Bureau:

Extended data

Weather symbols are special symbols representing various weather phenomena, clouds and sky conditions. Includes weather phenomenon symbols for observation and recording and weather graphic symbols for media communication.

When observing a certain weather phenomenon, meteorological observers should record the corresponding symbols in the "Weather Phenomenon" column of the observation record book of the day, except for a few phenomena, and also record the starting and ending time. Based on these symbols, combined with the intensity, coexistence and some characteristics of weather phenomena, a group of symbols that can be filled in weather maps are called cartographic symbols.

In order to make it easy for the public to understand and identify, a set of images and graphs representing weather phenomena has been formulated for TV or other public media.

References:

Baidu encyclopedia-weather symbols