The wind speed tends to decrease after sunset because at night the surface of the Earth cools much more rapidly than does the air above the surface. As a result of this difference in cooling ability, it doesn't take long for the ground to become colder than the air above it.

Why is it windy at night?

But there is another factor at work. Nighttime cooling sets up a temperature inversion, a situation in which cooler, denser air collects at the ground while milder temperatures prevail above. Such inversions effectively shunt large-scale, organized winds away from the surface, forcing organized winds aloft.

What time of day is usually the windiest?

These gusty surface winds usually begin in the late morning hours, peak in the afternoon, and end by early evening. Winds in the low-levels become much more uniform at night and in predawn hours.