This mid-level cloud took a wavy formation thanks to wind shear (specifically speed shear) whereby the Southwesterly wind under and above the cloud cover was blowing at different speed giving this cloud such form. The Maltese Islands were situated on the southern edges of a high pressure centred over Ireland. The first thumbnails shows another formation of altocumulus undulatus this time being in a distinctively different form because of the cloud being more isolated rather than overcast. The second thumbnail is a cirrus floccus cloud looking very flaky. Such form of high-level cloud might have been caused by abundant humidity at the upper levels but little instability.