If the air temperature is 26°C and the dew point is 14°C, estimate cloud base in feet AGL.

If the air temperature is 26°C and the dew point is 14°C, estimate cloud base in feet AGL.

• A. 4,000 ft
• B. 4,800 ft
• C. 4,600 ft
• D. 5,000 ft

Answer: (B)

Cloud base is set by how far the air must cool to reach the dew point and start condensing. A handy rule of thumb used in aviation is: cloud base (feet AGL) ≈ (temperature minus dew point) × 400, with temperatures in Celsius. Here the difference is 26°C − 14°C = 12°C. Multiply by 400 and you get 4,800 feet AGL. So the estimated cloud base is about 4,800 ft. This rule assumes near-surface conditions at standard pressure and is good for quick planning. A smaller temperature–dew point spread would yield a lower cloud base, while a larger spread would push the base higher.

Cloud base is set by how far the air must cool to reach the dew point and start condensing. A handy rule of thumb used in aviation is: cloud base (feet AGL) ≈ (temperature minus dew point) × 400, with temperatures in Celsius. Here the difference is 26°C − 14°C = 12°C. Multiply by 400 and you get 4,800 feet AGL. So the estimated cloud base is about 4,800 ft.

This rule assumes near-surface conditions at standard pressure and is good for quick planning. A smaller temperature–dew point spread would yield a lower cloud base, while a larger spread would push the base higher.