If actual temperature is 54 degrees Fahrenheit and dew point is 48 degrees Fahrenheit, estimated cloud base is approximately how many units (using the moist adiabatic formula)?

If actual temperature is 54 degrees Fahrenheit and dew point is 48 degrees Fahrenheit, estimated cloud base is approximately how many units (using the moist adiabatic formula)?

• A. 2.4
• B. 3.0
• C. 2.0
• D. 1.5

Answer: (A)

Cloud base height is tied to how far the air must rise before it cools to the dew point and condensation begins. When using the moist adiabatic approach, a handy rule of thumb is that the cloud base in thousands of feet ≈ (T − Td) in °F times 0.4. Here the air temperature is 54°F and the dew point is 48°F, so the difference is 6°F. Multiplying 6 by 0.4 gives 2.4, meaning about 2,400 feet above the surface. That’s why the estimate comes out to 2.4. The other options would correspond to different temperature–dew point spreads that aren’t present in this scenario.

Cloud base height is tied to how far the air must rise before it cools to the dew point and condensation begins. When using the moist adiabatic approach, a handy rule of thumb is that the cloud base in thousands of feet ≈ (T − Td) in °F times 0.4. Here the air temperature is 54°F and the dew point is 48°F, so the difference is 6°F. Multiplying 6 by 0.4 gives 2.4, meaning about 2,400 feet above the surface. That’s why the estimate comes out to 2.4. The other options would correspond to different temperature–dew point spreads that aren’t present in this scenario.