Why is flow over a car likely to separate as it passes over

Why is flow over a car likely to separate as it passes over the rear (e.g. rear window) but remain attached at the front of the vehicle (e.g. front windscreen)?

Solution

When a car moves in the forward direction, air coming in the opposite direction starts flowing over its hood, from where its velocity keeps on increasing until it reaches the top of the roof. Once it reaches the top its velocity starts decreasing as the air moves towards the rear position. The lower velocity at rear position leads to higher values of pressure (can be explained by bernouille\'s theorem). So higher pressure and turbulent air pockets at the rear position leads to the seperation of air from the car surface, which is not there in the front side, that\'s why seperation takes place on the rear side.