Instrument Rating Checkride Practice Test 2025 - Free Instrument Rating Practice Questions and Exam Preparation Guide

Surface winds generally flow at an angle to isobars due to the effects of surface friction. While in the upper atmosphere, winds can flow more parallel to isobars due to the lack of friction, at the surface, the friction between the wind and the Earth’s surface alters this flow.

As air moves from areas of high pressure to low pressure, the speed at which it moves is affected by objects such as buildings, trees, and terrain. This friction causes the winds to slow down and change direction slightly, allowing them to flow at an angle across the isobars towards lower pressure areas. The typical angle is approximately 30 degrees, though it can vary based on the amount of friction present and other conditions.

Understanding this relationship is important for pilots as it can affect flight planning and navigation, especially when operating near weather systems.