Estimating a convective cloud base
Pilots are often taught a quick relationship between surface temperature, dew point and the approximate base of convective clouds. It can be useful for understanding atmospheric moisture, but it is only an estimate and is not a replacement for an observed or forecast ceiling.
The temperature-dew point spread
As unsaturated air rises, temperature generally decreases faster than dew point. When the two meet, saturation becomes possible and cloud formation may begin. A larger surface spread usually suggests a higher lifting condensation level.
Common training shortcut
One common shortcut uses the temperature-dew point spread in degrees Celsius and multiplies it by roughly 400 to 500 feet to estimate an AGL cloud-base height. Different training references may use slightly different factors because the real atmosphere is not perfectly uniform.
24°C temperature, 14°C dew point
If temperature is 24°C and dew point is 14°C, the spread is 10°C. A rough 400-foot-per-degree shortcut suggests around 4,000 feet AGL. Treat that result as a reasonableness estimate, not as an actual reported ceiling.
Why the estimate can be wrong
Temperature and moisture can change with height, terrain can force air upward, weather systems can create layers, and clouds may not be convective. An overcast stratus deck may have little relationship to this simple surface-based shortcut.
Ceiling is a specific weather term
In aviation weather, a ceiling is based on the lowest broken, overcast or obscured layer rather than any cloud layer. A cloud-base estimate from temperature and dew point does not establish the official ceiling.
Use live observations
For flight decisions, check current METARs, TAFs and appropriate weather products. The estimate is best used as a learning tool or as a cross-check against observed conditions.
Related PilotDesk guides
Read METARs and TAFs · Density altitude