The sequence of vertical velocities in the subcloud layer before and after the formation of a
cumulus cloud are traced from multiple, simultaneous tethered balloon observations in the cloud
and mixed layers. Buoyant plumes originating at the surface serve to deepen the mixed layer with
the top of the mixed layer growing at a rate of up to 10 cm s-1. Cloud growth is initiated by the
mixed layer reaching the convective condensation level and not by discrete vertical velocity
plumes extending from the surface to the condensation level. Downward and upward velocities
are initiated at cloud base by the release of latent heat of condensation. Both upward and
downward velocities grow downwards from cloud base to near the surface. The magnitude of the
up- and downdrafts are the same (few meters per second) but the number of updrafts exceed the
number of downdrafts in and below cloud base by 50%. Mass balance must be achieved by
cloud-induced subsidence in the cloud-free air amounting to centimeter per second. The
cloud-induced subsidence suppresses the mixed layer in the cloud-free regions inhibiting cloud
growth and forcing cloud spacing. Cloud core transports exceed 2000 W m-2 but occupy less
than 1% of the total area. Less than 15% of the air originating in the mixed layer below cloud
base reaches cloud top (12 km).