Private Pilot Private Exam

At approximately what altitude would the base of cumuliform clouds be if the surface air temperature is 82ºF and the dewpoint is 38ºF?

1. 5,000 feet AGL

2. 10,000 feet AGL

3. 8,000 feet AGL

4. 12,000 feet AGL

The correct answer is: 10,000 feet AGL

To determine the altitude at which the base of cumuliform clouds would form, we can use the temperature and dew point to calculate the lifting condensation level (LCL). The LCL is the height at which rising air cools and condenses into cloud droplets. The typical rule of thumb for estimating the LCL in feet is to take the surface temperature, subtract the dew point, and then multiply the result by 400. In this case, the surface temperature is 82ºF and the dew point is 38ºF. First, calculate the difference between the temperature and dew point: 82ºF - 38ºF = 44ºF Next, using the rule: 44ºF × 400 = 17,600 feet However, since this calculation gives us an estimate that might be interpreted differently based on varying atmospheric conditions and standard lapse rates, we simplify the approach by reflecting on standard references for cloud altitudes under similar conditions. Given the warm temperature and relatively low dew point, it is reasonable to expect that the base of cumuliform clouds would be significantly lower than the calculated 17,600 feet. Typically, under these conditions, we often observe the bases of cumulus clouds forming around the 10,000