Opacus sub-species due to the low and heavy-looking dark base of the startocumulus clouds as seen in the foreground. A general high pressure was present over Malta as indicated by the widely-spaced isobars over the Central Mediterranean due to a `cool` high pressure persisting over the Islands. Althaugh such clouds look threatening with their dark bases, only brief light rain fell earlier that morning. This is a rare case whereby the clouds have formed in a blocking high pressure situation. Their formation was due to very steep lapse rate in the lowest 1.6km of the atmosphere as can be shown in the weather sounding and induced by a cool airflow around a high pressure system over the Balkans Peninsula contrasting with the warm sea surface temperature hence generating low-level clouds unable to grow by the stable air above it. The first thumbnail shows the activation of a cumulus cloud due to such process.