Why is the weather so changeable?

Mainly because of external forces, that is, energy from outside the earth. Specifically, it is the energy of sunlight, which leads to the uneven distribution of horizontal and vertical air pressure in various places, thus causing the flow of air, that is, wind. In addition, there are oceans and land on the surface of the earth itself. Because the specific heat capacity of water and land is different, the specific heat capacity of water is large. Under the same sunshine, the temperature of the ocean changes more slowly than that of the land, resulting in the pressure of the ocean being higher than that of the land, so the wind blows from the ocean to the land. The wind carries moisture in the air everywhere. When the air is cold, water vapor will liquefy, and when it meets the right conditions, it will turn into rain or snow, fog and other weather. Another factor is on land, because the terrain varies from place to place. The height of the terrain also leads to the change of temperature. The higher the altitude, the lower the temperature. Different temperatures will lead to different weather.

Personal opinion, for reference only. Please correct me if there is anything wrong.