Relative Humidity:

Humidity is the measure of the amount of water vapor in the air. The percentage of water vapor in the air compared to the maximum amount the air can hold is called the relative humidity. As you can see warmer air can hold more water vapor.

Relative humidity can be measured using a psychrometer. It has two thermometers, a wet-bulb thermometer and a dry-bulb thermometer. The bulb of the wet-bulb thermometer has a cloth covering that is moistened with water. Air is then blown over both thermometers. Because the wet-bulb thermometer is cooled by evaporation, its reading drops below that of the dry-bulb thermometer.

On the other hand, if the relative humidity is high, the water on the wet-bulb will evaporate slowly and the wet-bulb temperature will not change much. You will be using a relative humidity chart to record the percentage of the relative humidity. When the relative humidity is high there is a greater chance for precipitation. When the relative humidity is low there is a lower chance for precipitation.

Directions on how to use the Relative Humidity chart: When given wet and dry bulb readings. Dry bulb= 28 degrees Wet bulb = 14 degrees 1. Subtract the wet bulb reading from the dry bulb reading. 28 - 14 = 14 (difference) 2. Use the chart by locating the dry bulb reading (28)on the left hand side of the chart and lining that up with tthe difference (14) on the top of the chart. Therfore the relative humidity is 17%. Little chance of precipitation. When the relative humidity reaches 100% then it will rain, snow, sleet or hail.