Using a Skew-T log(P) diagram, a dispatcher determines the convective condensation level (CCL) for a departure airport. The CCL represents:
- AThe height at which a mechanically lifted, unsaturated parcel cools along the dry adiabat to reach its dew point
- BThe height to which surface heating must raise a parcel's temperature before it becomes saturated and cumulus clouds can form spontaneously
- CThe freezing level where supercooled water droplets begin transitioning to ice crystals
- DThe base of the lowest stratiform cloud layer reported in the current METAR
Show answer & explanationAnswer & explanation
Correct answer: B. The height to which surface heating must raise a parcel's temperature before it becomes saturated and cumulus clouds can form spontaneously
The CCL is found by following the surface dew point's saturation mixing ratio line upward to its intersection with the environmental temperature curve; this identifies the altitude at which surface heating alone (without mechanical lifting) will produce saturation and convective cloud formation. This differs from the lifting condensation level (LCL), which describes a mechanically lifted, unsaturated parcel cooling along the dry adiabatic lapse rate.
Why the other options are wrong
- A. Describes the LCL (lifting condensation level), a related but distinct concept from CCL.
- C. Describes the freezing level, unrelated to condensation from surface heating.
- D. CCL is a theoretical height derived from the sounding, not a directly observed METAR cloud base.
Convective Condensation Level (CCL)
The height to which a surface parcel must be heated before it becomes buoyant and rises to saturation, marking the expected base of cumulus clouds formed by daytime heating.
- Found on a Skew-T by intersecting the surface dew point mixing ratio line with the environmental temperature curve
- Differs from the LCL, which applies to a mechanically lifted, unsaturated parcel
- The convective temperature is the surface temperature needed to reach the CCL
Memory trick: CCL = Cooking (heating) the surface Creates clouds Level