The Mediterranean Sea is almost entirely surrounded by land — Page 433, Lesson 398

I want to walk you through the Mediterranean Sea and its adjacent lands from a meteorological perspective — this is a key region for your ATPL studies because it sits at the crossroads of very different air masses and terrain. Let’s start with the geographical considerations. The Mediterranean Sea is almost entirely surrounded by land. That simple fact drives everything. Compared with the land, the sea will be relatively warmer in winter — that gives unstable conditions above it. In summer, the sea is relatively cooler than the land, which gives stable conditions above. So during winter, surface air tends to flow in from the surrounding land areas toward the sea. During summer, it tends to flow out from the sea toward the land. Now, the terrain matters a lot. There are significant mountain areas to the north and to the west. In winter, the mountains to the north hold back much of the cold air from Europe and Asia. The high ground to the west resists the advance of polar front depressions — except through two key gaps: the mountain gaps in southwest France, and the Straits of Gibraltar between Spain and Morocco. To the south, there is no mountain barrier to prevent dry dusty air from the Sahara desert spreading north — except the Atlas mountains in the extreme southwest. Let’s move into winter pressure systems. The first type I want to cover is the Mediterranean front depression. The Mediterranean front lies east-west along the centre of the Mediterranean. It is formed by inflowing cold cPc air from the north — that’s continental polar cold air — and inflowing less cold cTw air from the south — that’s tropical warm air over water. Air is forced to rise along the convergence line, forming frontal depressions in the west. These depressions move eastwards along the frontal divide, driven by the westerly upper airflow. Now here’s a critical point: because the desert cTw air is dry, warm front and warm sector cloud does not form. So you get cold front weather only — no warm front or warm sector cloud associated with these depressions. Next, orographic or lee depressions. These can form south of the Alps over the Northern Adriatic and over the Gulf of Genoa. The Genoa Low can move south along the Italian coast, giving unstable weather. Lee lows can also form south of the Atlas mountains in Morocco with a cold west or northwest airstream, and then move northeast to enter the Mediterranean east of Tunisia. They can also form south of the Turkish Taurus mountains to form the Cyprus Low between Cyprus and Turkey. The Cyprus Low gives not only instability but is accompanied by northeast gales. Weak depressions moving into the area can become deepened and reactivated. These lows can then move eastwards into Lebanon and Arabia. Finally, the Siberian High. The Siberian High is well north of the region, but its cold outflow can reach the warm Mediterranean and cause instability. Let me show you the January weather icing chart and the July weather winds chart for this region — they’ll help you visualise what I’ve just described.