Formation of towering cumulus clouds as cooler air slides in towards the Ionian Sea from the Azores High over a much warmer surface. This causes such clouds to bubble up due to daytime heating and is indicated by ‘Thermal’ in the weather sounding below. The first picture is another photo of a donought shaped cumulus clouds (taken 13Oct17 morning) which are known to take many shapes. If the airmass had been unstable with a low pressure system such weather sounding was ideal for cumulonimbus clouds to develop. That week was dominated by a huge high pressure system as hurricane Ophelia pushed the Azores High eastwards with its central pressure over Central Europe.