Why does wind tend to flow parallel to isobars above the friction level?

Wind tends to flow parallel to isobars above the friction level primarily because the Coriolis force is strong enough to counterbalance the horizontal pressure gradient force. In the atmosphere, the wind is influenced by the balance of these forces.

At higher altitudes, the influence of surface friction diminishes, allowing the pressure gradient force, which drives air from high-pressure areas to low-pressure areas, and the Coriolis force, which acts to deflect the moving air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, to come into play more effectively.

When these forces are in balance, the resultant wind does not flow directly from high to low pressure but rather moves along the isobars instead. Specifically, the pressure gradient force pushes the air towards lower pressure, but the Coriolis force deflects it to the side, resulting in wind that flows parallel to the isobars.

This understanding helps meteorologists predict wind patterns and behaviors in the atmosphere, particularly at cruising altitudes where frictional effects from the Earth's surface are negligible.