CAPE is predictable from large-scale environmental parameters

A recent study by Agard and Emanuel (2017) proposed a simple equation for a quantity that scales with convective available potential energy (CAPE) that can be directly calculated from a limited number of environmental sounding parameters without lifting a hypothetical air parcel. This scaling CAPE was applied in a specific idealized framework, but the extent to which it can predict true CAPE in the real world has not been tested. This work uses reanalysis data over the U.S to demonstrate that this scaling CAPE does indeed scale very closely with CAPE, following a linear relationship with a scaling factor of 0.44. We then explain why they scale together via a step-by-step derivation of the theoretical assumptions linking scaling CAPE and real CAPE and their manifestation in the historical data. Overall, this work demonstrates that CAPE can be predicted from large-scale environmental parameters alone, which may be useful for a wide range of applications in weather and climate.