FAA Ground School Practice Test

At approximately what altitude would the pilot expect the base of cumuliform clouds if the surface air temperature is 82 degrees F and dewpoint is 38 degrees F?

1. 8,000 ft MSL

2. 10,000 ft MSL

3. 12,000 ft MSL

4. 14,000 ft MSL

The correct answer is: 10,000 ft MSL

To determine the altitude at which the base of cumuliform clouds typically occurs, meteorologists use the surface temperature and dew point to estimate the lifting condensation level (LCL). The lifting condensation level is the altitude at which the air becomes saturated, leading to cloud formation. In this scenario, you have a surface temperature of 82°F and a dew point of 38°F. The temperature-dew point spread is significant, at about 44°F, indicating that the air is relatively dry, and it will take a considerable lift to reach saturation. The general rule of thumb is that for every 1,000 feet of altitude gain, the temperature typically drops about 3.5°F. To find the approximate altitude of the cloud base, the following formula can be used: LCL (in feet) = (Temperature - Dew Point) * 1,100 Calculating it with the given numbers: LCL = (82 - 38) * 1,100 = 44 * 1,100 = 48,400 feet However, this result indicates the LCL calculated directly from the numbers may seem too high for typical conditions, so we simplify using averages: A practical approach indicates that, in general, a