by Jonathan M. Stern
Moisture in the Air
Another factor that affects weather is the moisture content of the air. Generally speaking, dry air yields good flying weather whereas moist air results in poor flying conditions.
The amount of moisture that the air can hold increases as the temperature of the air increases and decreases as the temperature of the air decreases. When air cools to the point where it can no longer hold its moisture, it reaches its saturation point, the moisture condenses into water droplets, and the relative humidity is at 100 percent. This critical temperature is called the dew point. When the temperature is within several degrees of the dew point, clouds and/or fog result. Clouds are composed of small droplets of water or, in the case of high clouds, ice crystals.