Leaves and small twigs in constant motion.

Amount of moisture present in the air relative to the maximum amount of moisture the air can contain at its current temperature.

Pressure is the weight of the air in the atmosphere. It is normalised to the standard atmospheric pressure of 1,013.25 mb (29.9212 inHg). Higher pressure is usually associated with sunny weather, lower pressure with stormy weather.

The temperature to which the air needs to be cooled for moisture to condense, for example, as dew. The higher the dew point, the more "muggy" it feels.