Formation of a distant roll cloud towards the north as a cold front was passing over that area as indicated by the SLP chart on the fourth thumbnail. Specifically, the roll cloud is known as cumulus mediocris arcus because some of its tops was clearly visible and did not look towering to be congestus. Normally, a gust front is associated with such types of clouds. However, the wind over the area did not increase and gusted at a constant speed of just 28kmh, perhaps that cloud feature was distant or could have been radiatus as the airmass following the cold front was unstable producing cumuliform clouds later on. However, contrary to normal cold fronts, this particular front produced nimbostratus praecipitatio clouds with precipitation reaching the ground and which in this photo it was clearing being recognized as such due to its lack of features. Nimbostratus might have indicated that the cold front was moving very slowly and that the airmass involved was stable given the normally cool SST found during early April. The first thumbnail is a wide single shot photo showing the background cloud covering the whole horizon whilst the second thumbnail depicts a change in the nimbostratus cloud cover possibly transitioning into another cloud species as the prolonged rain event was ending possibly showing undulatus-like features forming. The third thumbnail shows the weather sounding around that time proving the initial stability of the airmass and that cumulus clouds were possible at heights between 0.42km and 3km including some wind shear. Due to other clouds, it was not possible to decipher which was the roll cloud from the visible satellite image on the fifth thumbnail but is able to prove the SLP chart correct.
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