Explain  why surface winds are different during day and night?

Sounds like gradient winds. I'm learning more and more how the atmphisphere works. A strong mid latitude  storm  has a strong pressure gradient and the difference between a strong high pressure and strong low pressure tightens the pressure gradient( like squeeze play between the two).  Those winds as you described are from a major storm system not individual storms. As o have learned strong sustained winds are from horizontal pressure gradient in a midlatude storm or difference between  high and low pressures. The strong gusts are thermals or gravity waves mixing the winds to the surface from the stronger low level winds aloft( surface winds not effected by friction). As the sun goes down the thermals dissipate and a temperature inversion sets up. Cold air at the surface and warm air aloft. Cold air cannot rise and the plb increases at night as well. The sustained winds diminish at night too for some reason. However,  a strong  midlattitude  storm the sustained winds stay strong day and night. I think because the atmosphere is well mixed. The gusts at night and day during these conditions are from gravity waves and mechanical turbulence and friction. Sun will enhance gusts further in strong mid latitude storms but most of the time its cloudy and its during the spring,  fall, and winter. If there was a strong midlattitude storm in the summer the gusts  would be really magnified with the strong  sunshine thus making strong thermals. Thermals are stronger in the summer but pressure gradient is weaker in the summer. In the winter it's the other way around.

Wind strength is related directly to the horizontal pressure gradient.

The stronger the gradient the strong the wind.

Gusts result from the transfer of momentum from aloft to the surface.

In late afternoon ... a low-level temperature inversion develops in the planetary boundary layer as the ground cools while the air above remains warm.  The inversion prevents higher momentum air from mixing to the surface.

High pressure does not crush thermal.  Subsiding air in the HIGH acts to trigger thermals.

Feel free to ignore the majority of posted answers b/c they're all pretty much BS ...

During the day when the sun warms the surface it creates heat. warmer air is lighter than cold air so as a result the warm air rises and the cold air sinks. It creates a difference in atmospheric pressure  and due to the difference in atmospheric pressure wind is created. 

Simplistically, temperature.

Study meteorology or watch the Weather Channel a while or search Internet how winds work.