Important forces at work in the atmosphere I. Pressure Gradient Force - directed from higher pressure towards lower pressure at right angles to the isobars. Cold air aloft is normally associated with low heights. Surface Pressure chart - near the earth's surface the pressure decreases by about 10 mb for every 100 meter increase in elevation. In the northern hemisphere lower pressure is to the left. Winds blow counter clockwise around a low pressure system and clockwise around a high in the northern hemisphere.
Friction always acts in the direction opposite to movement.
If there is no movement friction is zero. The magnitude is a function of the type of surface. Friction is small over a frozen lake and strong in forest. Near the surface, friction reduces the wind speed, which reduces the Coriolis force. The weaker Coriolis force no longer balances the pressure gradient force and so the wind blows across the isobars toward lower pressure.