Why are desert nights sometimes surprisingly windy?

After sunset, desert ground cools fast and the air near the surface becomes denser. This can set up local pressure gradients between valleys, slopes, and open plains, producing evening or nighttime winds. Large deserts also often sit in regions with strong regional wind systems, so the dry, exposed terrain offers little resistance. When vegetation is sparse, even moderate wind can pick up dust and sand. That is why dust storms and blowing sand are common hazards in arid environments.