If the Earth was stationary...

air from an area of high pressure (Anticyclone - Near Right) would flow towards an area of low pressure (Depression - Far Right), like a stream flowing down a mountain side.

The Evolution of a Depression

The waters around the British Isles lie in a unique position. We are the first land mass Atlantic weather reaches; to the North there is the cold dry Polar air mass and to the South and West is the warm, moist maritime air mass. With Europe lying to the East we sit at the crossroads of Europe's weather.

Somewhere on the line separating a cold air mass and a warm air mass, an undulation forms which then becomes a centre of low pressure. In two or three days the depression deepens, and grows during the following four to six days.

As the depression follows its path from west to east, the cold front overtakes the warm front and turns into a spiral around the centre of the depression.


...But the Earth does rotate!!

Owing to the effect of the earths rotation, the air is deviated and flows in a spiral (clockwise in the northern hemisphere)

images show effect on an Anticyclone or a Depression.