If the photographed cloud is identified correctly, then it must be one of the rarest clouds ever to be seen over the Maltese Islands.

According to the National Weather Service in the USA, a horseshoe or moustache cloud occurs when rotating air or shearing horizontal winds create spin. Wind shear, or changing wind speed and direction with altitude can help to create spin. Gently rising air can then force part of the cloud upward. The first thumbnail is how the same cloud looked minutes earlier and the second thumbnail is how the same cloud developed after some 20 minutes following the photographed cloud and before it finally dissipated.

These clouds could have been some form of altocumulus lenticularis as mid-level clouds were observed at that time and which were described here “Ac lacunosus1“. The weather sounding on the third thumbnail seems to confirm the ideal atmospheric conditions for horseshoe clouds to form as described by the NWS. A gently rising air is shown as ‘Thermal’ in the weather sounding which happened due to very strong sunshine acting over a cooler airmass that arrived over the Islands on the previous day. This would have then been inhibited from rising due to convective inhibition, LCL of the weather sounding allowing wind shear indicated in the violet colour to take over the cloud formation forming it as it was. Notice how the clouds on the first two thumbnails were extremely layered on their top confirming my hypothesis. The fourth thumbnail shows the freezing level at athat time indicating the presence of a relatively cold airmass whilst the fifth thumbnail shows the presence of a weak high pressure system forming over the Gulf of Sirte after a previously deep low pressure system effected the southern Tyrennhian Sea.

More photos of the clouds of the day are available upon request from c.caruana@maltaclouds.net