The altitude at which clouds form is based on the dew point and the temperature of the air being lifted. The dew point is the temperature that the air must be cooled to in order to see clouds develop. At the beginning of a flight, the flight station operator can tell you the dew point. A formula which uses the dew point can be used to calculate the altitude of the bottom of the clouds, or the cloud base. To find the base altitude of the clouds, subtract the dew point from the ground temperature, divide by 4.4, and multiply by 1,000. The formula is expressed as: ((Surface Temp - Dew Point)/4.4) x 1,000 = CLOUD BASE

The answer gives you the altitude where clouds form. There is also the lapse rate, which tells you how much colder it gets. For every 1,000 feet you go up, you lose 3.5o Fahrenheit (F) or 2o Celsius (C). For example, if it is 71oF on the ground, it is 67.5oF at 1,000 feet.

QUESTIONS

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Curator: Tom.Benson@grc.nasa.gov
Responsible Official: Kathy.Zona@grc.nasa.gov