A number of storms developed over mostly the central and Northern Suburbs of Sydney during the mid to late afternoon. With a reasonable CAPE (Convective Available Potential Energy) environment in place with ample moisture and heating, it only took localised convergence to push convection through the cap. Once it got through cells developed rather rapidly. However, it was the cells over the Northern Suburbs of Sydney that seemed to relish in the ideal environment developing rather high tops.
But despite this system of cells moving north towards the Central Coast, an outflow boundary developed through the central suburbs from this thunderstorm complex and focused new development southwest of Blacktown. This storm exploded with anvil rapidly developing. A rain-free base developed and the storm began to take on some inflow. However, due to the lack of shear, the cell collapsed after about an hour.