Formation of stratocumulus due to a level of humid air at 850mb height as indicated by the weather sounding. The surface cool air heated by the warm sea rose up to around 2000 metres but its ascent was slowed down due to poorer lapse rates. Instead the cumulus cloud spread more horizontally covering a large section of the sky. As per visible satellite image, a relatively cold Mistral wind was blowing over the area due to low pressure system generating these clouds upon moving over a much warmer Mediterranean Sea.