Why is it dry in high pressure area?

Because the formation of high pressure area (generally the temperature is lower than the surrounding area) is due to the sinking of airflow (vertical downward movement), the air will be heated when sinking, so that the air can not reach saturation, so clouds and rain can not be formed, so the weather is fine. At the same time, due to the sinking and heating of air, the ability of air to contain water vapor will be enhanced after the temperature rises, and the air will appear drier when the original water vapor cannot be increased.