1.Air will try to flow in a straight line from high to low pressure.
2. It cannot do this because the Earth is spinning, so it veers to the right.
3. Centrifugal force kicks in with the result that, at 2000 feet, where there is no friction, the wind tends to follow the isobars.
4. Below 2000 feet, because the effect of centrifugal force reduces, the wind will back by about 30 degrees over land (20 over the sea) and about 10 knots by the time you get to the surface.
Simples.
Phil