What is the expected change in surface winds while descending, when reported as 180° at 20 KT from 6,500 feet?

When descending from 6,500 feet with surface winds reported from 180° at 20 knots, it is expected that the winds will typically back and decrease.

As a pilot descends, they generally transition through different layers of the atmosphere where wind patterns can change. At higher altitudes, winds tend to be stronger and can be influenced by broader weather systems. As you descend towards the surface, you might encounter friction effects due to the terrain and obstacles, which can lead to a reduction in wind speed.

Additionally, as you descend, you may also notice a directional change, commonly referred to as "backing." This means that winds may rotate counter-clockwise from their original direction as you approach lower altitudes. In this scenario, instead of maintaining a constant direction and speed, there is an expectation of a decrease in both speed and a change in direction, aligning with the concepts of wind behavior in the lower atmosphere.

Understanding these changes is crucial for pilots, as they can impact flight performance during approach and landing phases.