What relative humidity means?
The warmer air is, the more water vapour it can “hold.” Dew point is a measure of how much water vapour is actually in the air. Relative humidity is a measure of the amount of water in the air compared with the amount of water the air can hold at the temperature it happens to be when you measure it. To see how this works, let’s use the chart below, which is adapted from Meteorology Today by C. Donald Ahrens, published by West Publishing. Air temperature in degrees C Water vapour air can hold at this temperature. 30 degrees – 30 grams per cubic meter of air 20 degrees – 17 grams per cubic meter of air 10 degrees – 9 grams per cubic meter of air These numbers, which apply to air at sea level pressure, are based on measurements over the years. They are basic physical facts. Now, let’s see how dew point and relative humidity work. Imagine, that at 3 p.m. you measure the air’s temperature at 30 degrees and you measure its humidity at 9 grams per cubic meter of air. What would happen if this
