A miniature formation of cumulonimbus cloud with its anvil, normally cumulonimbus incus, forming pouch-like features. This occurred because apart from the cloud reaching a stable level hence spreading outwards, in this cloud`s case, the descending cold air from the anvil met a parcel of moist air rising from the surface resulting in the appearance of its pouches on the anvil side. It was clearly a thunderstorm cloud. The first thumbnail shows a cumulonimbus incus cloud taken in the afternoon. The day saw continuous formations of such clouds primarily due to an upper-level cold pool of air dragging a polar maritime airmass from the Rhone Valley towards the Western and Central Mediterranean inducing lots of instability in contact with the much warmer sea surface. This weather situation was typical for the Winter months when the sea still retains its warmth throughout the season. The second thumbnail is another cumuliform cloud formation with a rainbow due to falling rain shower underneath it. The third thumbnail is the weather sounding showing an unstable but relatively dry air profile. Such dry air profile probably helped to generate single cell clouds which was easily photographed rather than the compact cloud cover. The fourth and fifth thumbnails show the large upper-level low bringing the very cold upper airmass towards the Mediterranean and the resultant discrete cumulonimbus clouds forming mostly over the open waters.