Cumulus congestus altocumulogenitus radiatus cloud classified as such because it formed out of early morning altocumulus castellanus clouds. These transformed into cumulus and eventually cumulonimbus clouds because they kept on growing and growing aided by the strong May sunshine. The satellite chart on the fourth thumbnail indicate that the clouds were locally developed. The first thumbnail shows a cumulonimbus anvil cloud developed from the growth of altocumulus with mammatus features and which produced thunder along with an isolated rain shower with large drops of rain.

The weather sounding on the second thumbnail indicated that mid-level humidity was below 70% hence did not show any cloud cover making cloud identification more difficult than usual but the surface pressure chart on the third thumbnail showed a solid black line indicating that a trough line had passed over the Maltese Islands. An airport weather report at the time of the photographed clouds showed that the cloud base was at an altitude of 1.5km, being the same level at which the weather sounding indicated a quasi-stationary anabatic warm front probably serving as the trigger for the storm clouds to begin forming at that level with the surface air remaining totally stable.