Formation of cumulus congestus clouds due to a cold airmass becoming unstable over the warm sea under a low pressure system which brought severe gales the day before.Click here `26Nov15 Mistral Severe Gale` for further details.  An upper-level trough was still present over the area which kept fuelling the surface low. The first thumbnail shows the development of a slanting cumulus blob due to wind. The second thumbnail is the weather sounding that althaugh not showing any clouds due to overall dry air, it indicates very steep lapse rate which is enough for any evaporating warm sea water to quickly generate cumuliform clouds into the cold airmass. Such weather situation is more normal for the Winter months rather than late November.