Drone Pilot Practice Exam

What is the approximate height of the cloud base when the surface air temperature is 86 degrees and the dew point is 81?

1. 800 feet

2. 1,000 feet

3. 1,136 feet

4. 1,500 feet

The correct answer is: 1,136 feet

To determine the approximate height of the cloud base using the surface temperature and dew point, the formula used is often referred to as the "Lifting Condensation Level" (LCL) calculation. This formula approximates the height at which air becomes saturated and clouds begin to form. The general rule of thumb for estimating the cloud base height in feet is to use the difference between the air temperature and dew point. Specifically, for every degree Fahrenheit of difference between the surface temperature and dew point, the cloud base is approximately 1,100 feet above the surface. In this scenario, the surface air temperature is 86 degrees Fahrenheit, and the dew point is 81 degrees Fahrenheit. The difference between them is 5 degrees (86 - 81 = 5). Multiplying this difference by approximately 1,100 feet gives an estimated cloud base height of about 5,500 feet (5 x 1,100). However, to put this into proper context, when assessing the options provided, it seems like there could be a misinterpretation in the given choices relative to typical ranges for common surface temperatures and dew points. Given the typical behavior of the atmosphere under these conditions, choice C, which states 1,136 feet, is