A beautiful and unusual cloud formation at sunset on this day with the cloud looking almost like a very large funnel. On the ground, it did not produce any precipitation or severe weather. The weather situation of the day is explained in the next photo and also there was a strong overhead jet stream. When I queried about this cloud photo online, the following answers were given: 1) Mr. Jesse Ferrel (B.Sc. in Meteorology) -> Yes I do believe it is Altocumulus perhaps two layers with the Virga above. 2) Accuweather -> Classifying clouds can often be difficult, and in cases such as this subjective — but one possible classification, and the preferred one if for no other reason than simplicity is cirrostratus undulatus. Alternatively, cirrocumulus castellanus, cirrocumulus stratiformis or even cirrostratus overlayed on altostratus could be considered. To begin with, the weather sounding taken at 12Z (14:00 CEST) showed 3 cloud layers being Stratus (actually Cumulus clouds were observed in the photo probably at the height indicated by the sounding of around 0.55km), Altocumulus covering altitudes between 1.74km and 4.33km and high-level clouds between 8.23km and 12.53km. Wind shear of the former cloud level as calculated by Jeff Haby formula was 6 units which means lots of wind shear while at high altitude where the high-level cloud was located little wind shear was present but the jet stream was a strong 130kmh. Given this detailed analysis from using the weather sounding, and that to form undulations in a cloud layer, it requires wind shear in order to make the whole air colomn rotate, I came to the conclusion that it was Altocumulus undulatus, althaugh the huge roll-like feature is very strange for an Altocumulus undulatus. It could also have been a peculiar combination of 2 different layers of clouds one altocumulus and other cirrus clouds just above it. Furthermore, a strong jet stream which was present on this day would form wind-swept high level clouds rather than rotation in the cloud layer given the lack of wind shear at that level. This cloud seemed to have been visible even from satellite imagery. The following thumbnails show another photo of the same cloud taken earlier before sunset, the weather sounding of the day and the jet stream chart. An 18Z (2000 CEST) sounding was also looked at but provided very little clouds that could have explained this unsual cloud formation for the Maltese Islands. The 850mb chart is also included in the thumbnails as the closely packed temperature lines might indicate a cold front at that level (1.5km) perhaps having triggered this cloud formation. Note: To calculate mid-level wind speed shear value, the wind values of 38 knots at 1.97km and 58 knots at 3.68km were used for calculation purposes.