Altocumulus clouds are as prevalent as stratocumulus or cirrus clouds, but altocumuli have been studied much less extensively. In this presentation we ask, What causes altocumulus clouds to decay? To address this question, we examine aircraft observations of a mid-level cloud that was measured during the Complex Layered Cloud Experiment (CLEX) field campaign. The liquid water budget reveals that the largest contributor to decay of liquid water is subsidence drying associated with the passage of a high PV anomaly. The smallest contributor is precipitation. The role of radiative cooling is interesting: liquid water is directly increased by radiative cooling, but this increase is offset by radiatively induced entrainment drying. It is not clear whether the net effect of radiative cooling is to prolong or curtail the lifetime of the cloud.