Why would there likely be low humidity when there is high pressure system in your area.

Humidity is defined as the amount of water vapor in the air. Air pressure is defined as the force that is exerted on Earth’s surface by the weight of air. On average, air consists of roughly 78% nitrogen, 21% oxygen, and 1% argon. The rest of air is composed of trace gases such as carbon dioxide, neon, and helium. When the humidity is high, the amount of water in the air is higher than normal....

Humidity is defined as the amount of water vapor in the air. Air pressure is defined as the force that is exerted on Earth’s surface by the weight of air. On average, air consists of roughly 78% nitrogen, 21% oxygen, and 1% argon. The rest of air is composed of trace gases such as carbon dioxide, neon, and helium. When the humidity is high, the amount of water in the air is higher than normal. As the amount of water vapor in the air increases, the amount of oxygen and nitrogen in the air decrease. Water is made of two hydrogen atoms and one oxygen atom (H2O). The mass of water vapor molecules is less than the mass of the diatomic oxygen (O2) and nitrogen (N2). Therefore, there is less force that is exerted on Earth’s surface. This results in a lower air pressure. Thus, as the humidity increases, the air pressure decreases.

The opposite is also true. As humidity decreases, the amount of water vapor in the air decreases. Thus, there is more of the heavy nitrogen and oxygen, which results in an increased air pressure. Therefore, low humidity results in a higher air pressure and vice versa.